Should I pass by const reference or by value?

[@youssefmohamedabbashabib613]

Absolutely good idea. Divide the videos into multiple topics 🙏

[@theuser1240]

+1

[@juny4351]

+1

[@wiseskeshom4673]

+1

[@phizc]

Yup. This is the first code review video I've watched, so it definitely works 😃.

[@AstuteJoe]

+1

[@robertmoats1890]

A completely agree with you that passing primitive data types by reference is not a great idea. It will most likely prevent compiler optimizations. However, I think its probably a good idea to pass custom types by reference, even if they are small. The reason being that their size (and internal behavior) can easily change in the future, without the programmer later realizing that these function parameters all need updated to reference types. After 20 years of programming, one thing I've learned is to treat everything I've touched as unstable and dynamic.

[@calengo454]

damn

[@seargd1]

This was definitely more easily digestible and focussed than 40 minutes of code review that goes in five different directions. I smashed like so hard on this that I almost dropped my phone.

[@Lockdheart]

I heartily approve of doing the code reviews by topic. If it tells you anything, this is the very first one of your code reviews I've ever watched--specifically because it wasn't ridiculously long, and I could see in the title that it was about something I might find useful. You might get fewer views per individual video this way, but I have a feeling you'll get *way* more total views overall.

[@m4l490n]

I don't agree, I think he'll get even more views per video because they'll be short and more focused.

[@emmanuelvazquez5036]

Same here. I once started like a 1h video of code review, but quickly I got lost and never finished. Instead, for this quick video I already entered knowing what was the topic, was direct to the point, easier to understand and, well, I saw to the end.

[@thecwd8919]

I agree with this

[@aronseptianto8142]

this is absolutely a better format, not only because my attention span is garbage but also it really helps to build a library of "advice" video that's easily searchable even without the context of the code review this kind of advice is quite rare in a normal beginner tutorial and StackOverflow can be quite asinine about it this way your video can reach a broader audience who just need specific advice

[@vitormoreno1244]

Divide by multiple topics, that will help your channel on the long term as more videos will popup on KZbin search. And that will help less skilled programmers(like me) to learn specific topics.

[@RelayComputer]

Just look at the assembly code my friend, I bet you will get a couple of surprises, particularly with private methods. Hint: the compiler does not always honour the argument passing convention you specified

[@andyyy1094]

can you go into a bit more detail? what exactly are you referring to

[@RelayComputer]

​@@andyyy1094 I mean that you can write code meant to pass or return parameters by value, particularly long structs, but the compiler may decide to pass them by constant reference if such parameters are not modified inside the function and the function is contained in the same translation unit (C static function, or C++ private method). Furthermore, even if the function is not private, some compilers can go a step further and create two versions of the same function, one to be called (often inlined) using references when invoked from the same translation unit (regardless of what passing convention you specified), and another one ready for external calls. However, what is said in the video is correct and programmers should keep with good practices and never assume that the compiler will optimise everything

[@urisinger3412]

Dont trust the compiler on everything, especially if you want to run things in debug mode.

[@RelayComputer]

@@urisinger3412 What you mean by don't trust the compiler? Compilers are by far the most trustable pieces of software in existence. Can't imagine the mess if it wasn't like that

[@urisinger3412]

@@RelayComputer dont trust the compiler to optimize every stupid thing you do, they dont catch everything and those little things can add up

[@m4l490n]

I just want to join all those that have said that it is an excellent idea to divide the code reviews into smaller videos focusing on one concept. It is super useful!!! Also, you get the opportunity to explain the same concept in multiple and different code sets which will greatly help understand better the concept, you know, by looking at it from different angles and use cases.

[@Spongman]

This video is good advice, it's basically F.16 in the cpp core guidelines: For “in” parameters, pass cheaply-copied types by value and others by reference to const. F.15 has a really good diagram that illustrates all the choices. IMO it's a good idea to keep your argument definitions 'const', even when receiving value types. Especially in larger methods it's useful to know for certain that a given argument hasn't changed. Also, don't use 'new', 'array'/'vector' would trivially give you the all-important move constructor for that buffer.

[@Balouxe]

This format is a good idea, and you could also add this video to the C++ series as it covers a pretty interesting topic that fits into it ! Cheers

[@battosaijenkins946]

Heheheh... i know fools who const reference everything even boolean types and I'm like... 🤦‍♂🤦‍♂🤦‍♂

[@stvreumi]

I like the idea of splitting the code review video by topic! It taught me a lot. Hope to see you sharing more videos like this in the future.

[@djazz0]

So happy I'm not coding in C++ anymore. I use Nim and it checks the size of what you pass and chooses by reference or value at compile time. So if you pass an object, it gets sent as reference if it's above a certain threshold. Ints gets passed by value unless you use "var" (mutable reference).

[@amayesingnathan]

100% love the shorter videos. Recently I haven't been able to find the time watch longer code review videos, so breaking them down makes it much easier

[@mateuszabramek7015]

That "it gots darker here" got me 😂

[@fabiannedelcu3492]

I really like the short, by topic code review!

[@anon_y_mousse]

This is one of the few times when I actually agree with the design of C++. Since references are mostly transparent you can start with just passing by value and should you change to a more complex object in the future merely change the signature to include a const reference and have little trouble. Some languages make the boneheaded decision of either removing pointers and explicit reference documentation and everything is a reference. Some make the equally boneheaded decision of making references explicit all around which basically means they're just pointers. C++ actually did it right here.

[@Spongman]

references are just non-nullable pointers with a '.' accessor instead of '->'. who knows why k&r chose '->' instead of '.', but hey now we're stuck with it.

[@Ich_liebe_brezeln]

@@Spongmanbecause it’s already used for normal objects. You can also use it with pointers but you gotta dereference them first, leaving you this (*obj).member And it becomes hard to handle when you deal with nested pointers like this: (*(*(*obj).member).attr).val So they invented -> to avoid typing the above obj->member->attr->val

[@Spongman]

@@Ich_liebe_brezeln you missed my point. I’m saying that k&r could have just used ‘.’ for pointer indirect without ambiguity, since pointers themselves don’t have members. Your last expression could easily have been ‘obj.member.attr.val’.

[@Ich_liebe_brezeln]

@@Spongman Oh well, now I get your point and I guess is not a bad idea. Maybe they wanted you to remember that you were dealing with pointers at all times… or didn’t really think that much about that.

[@willchris7654]

I think, at least for me, it'll be easier to learn and digest your videos in a smaller chunks format like how you use to do C++ tutorial. It'll also be easier to see what specific topic you're covering specifically and if later I need to come back to it, it'll be easier to search as well. Just my thought though. You're still one of my best mentor for programming :)

[@PuraTvOyun]

Great Idea go for it. That is the exact reason why I watch long code review videos. At any random time in a video, you give a specific knowledge for a specific situation that normal learning seriea doesn't even think about to teach us. For example this video enlighten me about r and l-values. Thank you for that. Learned C++ with your C++ series years ago and now I can develop custom tools for the games I make with Unreal Engine.

[@stavrosmalagaris3352]

Splitting a long code review into more specific and shorter videos is a fantastic idea. As you said anyone could focus on particular topics that may be intersted in and understand a topic better without being overwhelmed

[@decky1990]

Really valid topic! Varies in a lot of things - threads and coroutines make things slightly trickier, but nice video

[@Zarathustra0512]

fwiw, the "built-in C++ type" is std::uint32_t. uint32_t is a C alias that most (all major) C++ std library implementations happen to provide, but isn't part of the std

[@olo90]

Personally, both formats (longer video with timestamps) as well as short formats that are just focused on one part are fine. I'd say make the choice based on what gets more views (without having to resort to click-baity titles / screencaps with those "shocked face" looks).

[@justindavis5960]

Definitely prefer this format more than a longer video as it is easily digestible. It could also be more useful for people who just need information on a specific topic

[@BlazingMarauderDCUO]

Explaining the "why" of anything is extremely valuable, at least imho. throughout all of your content that I have watched, the most enjoyable is when you explain quite trivial things but explain the reasoning at a really low level.

[@stefanhellwig-lp4rg]

I also like the idea of splitting the code review into shorter videos. This let‘s one pick the topics of interest quickly and it‘s also easier to „digest“ ;-).

[@TobotriebNightcore]

I like the Qt style: pass c++ (std)types by value, Qt objects by reference, and Qt objects where you transfer ownership by ptr

[@sasha9245]

It's also nice to understand the difference between passing by value as 'const uint32_t' or 'uint32_t'. Assuming the argument is in a register, for 'const uint32_t' compiler is safe not to create a copy, while for 'uint32_t' it might allocate another register as this argument might be changed inside a function. For example: uint32_t sum(uint32_t n) { uint32_t sum = 0; while (n > 0) sum += n--; return sum; }

[@bavovna_v_maskve]

I agree that having separate videos on specific topics is better. I'm currently struggling with my side project in C++, and I can say I'm already pretty comfortable with templates and even type traits-topics considered quite complex-even though I've never used them before. But I still often struggle with basic things like passing by value, reference, or pointer, or knowing when it's better to use shared_ptr or unique_ptr, move semantics, etc. Probably that's because I've been employed as a Python developer for years, and I deal with abstractions and polymorphism with dynamic types every day, but some basic C++ concepts are new to me and others like me.

[@FatalExceptionz]

Another thing to consider is that unnecessary passing by pointer/reference can also prevent the compiler from making certain microoptimizations

[@DaddyFrosty]

Oh shit I thought Const ref would help as opposed to impede that

[@teranyan]

@@DaddyFrosty It is exactly like that. Using const ref gives the compiler perfect information, it can choose to copy or not the uint. People who don't understand this and just spit out the "pass small types by value" ideology from 30 years ago, are frankly clueless. Const reference isn't some promise to use a pointer, it represents the abstraction of a read only object that already exists somewhere.

[@piechulla1966]

@@teranyan C++ Core Guidelines F.16: For “in” parameters, pass cheaply-copied types by value and others by reference to const

[@ABaumstumpf]

@@teranyan It depends on the function. Say something like "void multiplyVectorByValue( std::vector& vec, const& val)" - iterating over the vector and multiplying every member by val. here passing by reference can be a serious detriment if the compiler can not proof that "val" is not part of "vec" - cause then it has to re-load val on every iteration, preventing any loop-hoisting or vectorisation.

[@TheJohndward01]

The part of the video where you said you should probably make an entire video about, I think it was around 2:15, that would be very helpful. The CPU is still very much unknown to me. And individual videos would be great especially as a playlist too.

[@animarain]

Yes!!! Please do that! Splitting it into parts and explaining different topic on each video would be so much helpful!

[@matpietrzak]

Good idea. Shorter videos but more specific targeting a given concept or issue. It 's gonna be more interesting.

[@marcio603]

I agree that dividing the videos will make them more "digestable" but your content is so good that I wouldn't mind to watch hours of video... I work with C++ nowadays and there some videos that I have watched several times... Thanks for the sharing your amazing knowledge.

[@ktoztam]

As someone who was actually wondering about this thing in particular I very much aprove the idea of making code reviews as by topic rather than long format they used to be.

[@artie5913]

4:10 what if someone adds something big(like a bunch of strings) later in this CustomType? I don't think you want to fix every pass by value after this

[@Firepipproductions]

I would pass a custom struct of two 32 bit ints but not a 64 bit int as const ref. Conceptually you are right about the pointer argument, but especially if you make it const, the compiler figures it out to be the same. The custom struct might be 8 bytes now, but could be expanded. It's also just more consistent to have built in types by value and custom stuff const ref. If you use that pattern, passing a custom small type by value will look jarring. Also, as you mentioned yourself, const ref can take an rvalue. This means it doesn't actually have to treat the value as a pointer. Does 2 have a memory location? Not until the compiler decides what to do with it. In fact, const ref tells the compiler to do what is most optimal actually. It might just in place the argument as value wherever it is used for instance.

[@Sebanisu]

static_assert(std::is_trivially_copyable_t); Type trait can be used to test if your type is trivially copyable.

[@antonincarette8928]

Very good idea - the fact to show more shorted (but specific) videos is (imho) more interesting and more appealing than big review videos.

[@antonincarette8928]

@thecherno3 OMG thank you! What did I won?! I can’t believe it! It is amaaaaaaaaazing! I hope you’re not a fake OMG! I hope it is a house! Is it a house? Or a 35 levels building in the middle of Central Park?! Or, more amazing, 15kg of twinkies!!!! I hope this is not fake OMG! WHAT IS A DM? HOW TO DM? WHAT IS THE PURPOSE OF LIFE?! WILL « TRON 3 » BE A GOOD TRON SEQUEL? SO MUCH QUESTIONS!!!!!!!

[@arispacegirl]

making short code review responses that address very specific topics would be perfect for...well, shorts! I've seen a couple channels try out short "tips & tricks" videos around code and they've been very useful!!

[@KristofNachtergaele]

This format would indeed be better than the massive code reviews, i skip those but this had a title that described what was being talked about and interested me and turned out to be useful.

[@markrudford3143]

Well, you only need to use a const if that reference or data type is needed else ware in the code file. If not then go the value type route if it is not used anywhere else but once to declare a value. Dynamic vs static values used once or more. Depends..

[@davedobson9801]

The only thing I'll say in defense of the const reference approach is that occasionally I create a method, forget to use a reference on the parameter which makes a copy, then try to modify the parameter inside the method, which does appear to work, but find upon return that the parameter is not modified. That's why I prefer to use const reference instead of value. It makes it more clear for me and for others that the parameter is not intended to be modified and you have to work harder in the code to actually make it happen. Team programming sometimes requires that you write code slightly less optimally in favor of clarity. So in other words, never pass by value, pass by reference, and use const when the value is not to be modified.

[@TjSBMD1810]

Exactly this is, how i also got "teached" how to handle this. This video actually surprised me saying const ref arguments are bad ^^

[@sourestcake]

But wouldn't just const work in this case without the reference?

[@chases4951]

Have you ever seen a case where passing by reference was better due to the reduced set of memory pages being used? I could imagine a case where it would help with TLB hits in the CPU?

[@simonfarre4907]

I've seen code passing things like string view by const string_view&. Most views, should be passed by value as they often consists of a pointer and length - this usually fits in a wide 128 bit register. This gives the compiler a possibility to optimize. As soon as you use references, you are essentially aliasing data, which hinders some optimizations. And yes, when your type has raw pointers to data you want to shallow copy - because if they hold raw pointers, they should be non-owning views. Someone else owns the data. If not, use shared ptr, and in that case, DON'T create a constructor. You want to eliminate ALL custom constructors always - it should be very rarely when you write custom constructors.

[@mikefochtman7164]

I think the 'const' is a key part. If the function doesn't need to modify it, then passing by value is fine. (and if the function is const-casting the const away to modify the value, well take that programmer out back and have a talk with them about why they made a function interface that lies) If the function had to modify, then a reference/pointer would be necessary. And if you can pass by value, there should be a bit of performance since each time the function accesses it, it doesn't have to dereference the ptr type over and over again. But that would depend just how often it accesses the parameter.

[@0xKakashi]

Never thought of this whenever using passing by const reference. Cherno sir 👌

[@kent8547]

I look forward to your bigger video on this :) I also enjoy this style of code review more, it's more descriptive to what the video goes over

[@sanduchicu7545]

Great video as always! The short form videos I think are a lot better because, as you said, the video is more on-topic but not all over the place. However, I think for every code review you should first make a video to overview the project and show the improvements that you would do, maybe explaining briefly (not focus on just one improvement, like the flying dog game video) and then make separate videos on every important topic, explaining it in detail (just like you did in this video).

[@malckhazarsteamcat9817]

Oh, my dear Cherno. 1. Roughly at 1:20 you said that const reference is converted to ptr. Actually, not just a "ptr *", but "ptr * const". 2. Passing argument to a function depends on ABI. If your ABI declares that all arguments must be passed via stack - then yes, small types converted to pointer will take more memory. In old ABIs agruments was always passed via stack (see Intel x86 ABI as an example). In modern ABIs arguments mostly are passed via registers which always have same size. Only data with sizes higher than register size always passes via stack. The main difference here is number of accesses to a memory holding the value and it will be "long" if variable located in different memory page, which will have to be kept in RAM. 3. At ~4:59 you saying that "type is not trivially copyable" is an issue of passing by value. This is not the sole reason. If your type is trivially copyable, but is a big sized (too many members/fields) - this is also an issue for passing by value, because you'll eat all the stack.

[@Raspredval1337]

clearly breaking abi is not an issue, if you're still in development, just recompile the binaries

[@reductor_]

With (2) if your passing by reference then the reference needs to point to a place in memory, if this is something that was previously just a local variable this is going to force it onto the stack just so that it can be passed as a reference to the called function. ABIs difffer a fair bit it's not just size that impacts things but also if the type is trivial, if the ABI splits structs (like System V), then you have some which don't have many registers for arguments like MS ABI Also 32-bit x86 is pretty much dead these days for any game you ship and not worth worrying about, everything targets 64-bit now.

[@malckhazarsteamcat9817]

@@Raspredval1337 You can break ABI only if you write the call by hands in Assembly language. ABI is the convention which is followed by compiler, not the developer.

[@anon_y_mousse]

@@malckhazarsteamcat9817 You mean the platform. The compiler just targets the platform, so if the convention used is wrong it's because the compiler targeted the platform incorrectly.

[@malckhazarsteamcat9817]

@@anon_y_mousse No, you mistook. ABI (or Application Binary Interface) is a convention declaring the order how calls should be made in Assembly. It is included in that you call a "platform", but, technically, it does not restrict you to use other orders of calls inside your code. The problem will arise only after you violate ABI used in compilation of other binary parts of your app - libraries, system calls, etc. Inside your code no one can restrict you from writing the call to your function in Assembly.

[@harleensingh2531]

As you said, a big video on this would be really cool. Thanks for all your work :)

[@Raspredval1337]

So, if we can efficiently pass stuff by value that is

[@orangasli2943]

For anybody confused.. for 64-bit application.. one memory address can store up to 64-bits of information or data.. or specifically 2⁶⁴-1..which is an unsigned long.. If you have a class that contains x,y,z values i.e a `3dVector` class.. this data requires 4*3*8=96bits.. So this requires two addresses to store the information.. whereas if you have a pointer variable.. it will only require it to store the information in one address instead of two.. so the process is faster .. And so does the game

[@giornikitop5373]

with modern cpu's (

[@sourashismondal5060]

Hi, can you please make a detailed video of how virtual table works in the context of virtual functions?

[@avtem]

i really liked this one. It's short and it's about one specific topic.

[@ИнякинАлександр]

На современных процессорах объекты размером до 8 указателей (32/64 байта) можно смело передавать по значению. Без глубокого копирования указателей на кучу, естественно.

[@YeloFelo]

Love this style of broken-up code review, but it would be nice if there was some indication that this is actually a code review, like maybe on the thumbnail

[@ciCCapROSTi]

I wanna add, if you are consistent with your pointers, a raw pointer can express a non-owning, nullable reference. So it's a great way to have something point to someone without copying it, as long as you can be sure the object stays alive, like it's allocated in main or the encompassing object or something. Otherwise yeah, weak_ptr, but shared is dumb.

[@thelemonman2271]

Holy shit I searching for something like this just a day or two ago. Chreno-sama smiles upon me 🙏

[@mikefochtman7164]

Regarding monolithic code reviews vs snippets about specific coding issues, I vote for the latter. Bits of info about specific topics seems better (IMHO).

[@JohnWasinger]

I listen to your videos as I drive. I like that the signal to noise from your talks is quite high. I’m not talking about static here. I feel like I’ve learned a lot from just listening to you. Some CppCon presentations are very useless to just listen to.

[@yousufazad6914]

Yes, please. Short videos on a specific topics

[@brunooliveirasoares7489]

Such a good idea! Please, more of these short videos!

[@TheRealFFS]

Agree with others, I think the length and content of this video is much more preferable to your longer videos. Easier to digest etc.

[@vsevolodnedora7779]

I found it useful, and I am more willing to watch a short video about a specific problem/thing in the code.

[@perkele1989]

Here’s a hot take; put the const to the right of the variable name. Imo it’s more correct, despite being more uncommon. Const is parsed from right to left, with the only exception being if it’s leftmost, then it’s parsed the other way. So people are actually doing an exception to the rule all the time.

[@masheroz]

West Const for life

[@dXXPacmanXXb]

9:43 yes! this is a fantastic idea. I only clicked on this because the title was interesting. I never click on code review videos

[@AntoniGawlikowski]

By topic sounds (and works in this instance) great!

[@DeGuerre]

This is probably for the Big Video(tm), but passing these small POD types by const reference can have big performance implications beyond the call site. A CPU register does not have an address. Taking the address of a variable means that, for at least some of its lifetime, that variable cannot be stored in a register, since the function you called might want to retain the reference somehow. C++ has a now-deprecated keyword, "register", which makes it an error to take the address of some variable. That was useful behaviour. ADVANCED KNOWLEDGE: Even for a heavyweight object, you may still want to pass it by value under some circumstances, most notably if the callee is going to take a copy. This moves the copy to the caller (which may result in the copy being avoided altogether if the value is an lvalue); the callee can use move semantics rather than copy semantics.

[@DummyFace123]

Beyond this, its just unintuitive behavior to ref a constant. Reffing a constant sort of mimics a static readonly. And if you're seeking to save memory in this way then a static readonly is the way to go. If we look into why string.Empty is a static readonly rather than a constant, it has to do with using it from unmanaged code not marking it as a literal. _"The Empty constant holds the empty string value. We need to call the String constructor so that the compiler doesn't mark this as a literal. Marking this as a literal would mean that it doesn't show up as a field which we can access from native."_

[@svenbtb]

These smaller code reviews are really great, seeing examples of topics (like passing by value vs reference) within the context of a project is really helpful, especially for someone who's learning and practicing so I know not to make similar mistakes, ect. Plus exactly like you said, just seeing a 40-80 min "Code review for Flying Dog" generally makes me not want to watch so much lol

[@Micah20001]

nice video. Anyway I watched a lot of your videos and one think that i will remember for sure is "kind of", "kind of", "kind of"

[@DaveMacara89]

Very insightful as always Cherno thanks!

[@guilhermedabolsa927]

Good idea Cherno! Clicked on this vid because it was not 01h and 40min long for example =)

[@twipps7700]

thank you for clearing this confusion on my part!!

[@TheBestNameEverMade]

So an aspect that was forgotten here was the speed of the compiler. In large project or large engines it's very important to forward declare things. So if it's a large file that gets pulled to include a variable in an it's not the hotpath seriously consider using a reference so the type can be forwarded declared instead... of course if you are not working with code that is likely to get very big don't worry o much. However c++ compilers can get very slow very quickly if everything is being included in headers which will mean less time for the dev to spend optimizing code that matters.

[@harleensingh2531]

I think dividing code review based on topics would be great!

[@aurinator]

Honestly surprised this isn't handled by the compiler.

[@arsnakehert]

Oh no, watching The Cherno's videos gets me excited about copying memory and pointers and whatnot in C++, I don't want to dive into this rabbit hole again *starts editing makefile* oooooooh nooooooooooo what have you dooooooooooone Chernoooooooooooo

[@cubevlmu385]

Fantastic topic, helps a lot about programming futures. Nice video

[@entusiast2000]

AFAIR, x64 compilers like to use __fastcall-based calling convention. In this case **maybe** there's no difference in **memory** used for the value/address transfer (if the value's trivial, less than a register width etc etc..).

[@antonpieper]

Good idea to split the review up👍

[@art0nsec]

I prefer to watch the code review split into smaller topics. Makes it easier to process and I search it, should I ever want to rewatch it.

[@alienrenders]

A lot of confusion in the comments. Been programming in C++ since before it had templates. To keep it simple, pass by value anything that's a primitive type or less than 8 bytes in size. Everything else should likely be by const reference. Now, there is a recent push to pass almost everything by value. Compilers are supposed to know what to do. But in practice, compilers aren't there yet. So just stick to passing primitive types by value and everything else by const reference. One sidenote is that on x64, only the first four arguments will be passed in registers. It doesn't change much for this topic, but it's good to know.

[@samuelmartin7319]

I like the idea of splitting up the code review my topic.

[@john.dough.]

love seeing this short and sweet!!

[@ohwow2074]

Basically anything equal to 16 bytes or less is better to be copied or moved. References are a bit expensive since they are pointers most of the time and thus need to be dereferenced and that can reduce the efficiency.

[@Raspredval1337]

Well, yes and no really. If the function is inlined then compiller should optimize that away. But it will not work here, cuz the class definition and implementation are kept separate, thus the methods are not inlined by default

[@ohwow2074]

@@Raspredval1337 as I said, "most of the time". Inline functions eliminate that problem. But rarely any function is inlined. So the general rule of thumb still applies: for types of sizes

[@vincentpieterse1694]

Hi Cherno. Love your work! Could you please do a c++ video on implementing a finite state machine?

[@MuggenHor]

It's not just about the size. The compiler is also allowed to perform optimizations on value parameters that it's not allowed to do on reference parameters. Specifically everytime that you call another function, from within the function that received it's parameters by reference, the compiler must reload the value of that referenced variable from memory. Because the referenced variable might have been changed. This problem doesn't exist for value parameters because they're local variables to which nothing else has access. Unless you give it access. And because calling a function that takes referenced to its argument gives access the same problem exists for the caller! I.e. references to cheap to copy objects are expensive on both sides of the function call barrier!

[@ABaumstumpf]

"the compiler must reload the value of that referenced variable from memory." No. That depends on the function and the surrounding context but by no means is the compiler forced to do so.

[@MuggenHor]

@@ABaumstumpf sure it depends. Specifically the value of that referenced variable needs to be used after the function call for such a reload to be necessary

[@aaronmacdougall]

The size of the pointer/reference isn't the issue. The indirection is a performance consideration as it will cause a pointer indirection when the data is accessed. I would recommend any basic types including __m128 be passed by value as the first 4 int and seperately float/simd arguments (depending on ABI) will be passed in registers, without copying to the stack and therefore pass a pointer. On Windows the x64 ABI prevents any structs larger than 64-bit from using registers. On other 64-bit operating systems and platforms a struct with two 64-bit ints can be passed through registers. This is why new C++ types such as std::span and std::expected perform poorly on Windows and Xbox. This is also the case with returning structs/classes by value.

[@vmarcelo49]

I liked this format, short videos are better to be referred later too

[@turner7777]

My opinion on the const ref is that it doesnt really matter, in fact, matter the case, it can be even better because its like ensuring that syntactically he wont use that variable to write to so he can only read from. As per the performance, with /O2 its almost identical, performance is the same. In one case it is performing operations on the registers directly (pass by value) and in the other its just dereferencing the address (pass by ref). So in both cases its the same amount of instructions, now the microinstructions can differ but i dont really think that is a factor if you want your code to look more "clean?"

[@reductor_]

The optimizer can't break the ABI, so a reference is still a reference, your still forcing a value which should be a register into memory (often on the stack), your still preventing the compiler from optimizing it when it can't see into other functions, while most code doesn't need to be fast there are definately cases where pass by value will make a difference.

[@xbz24]

very deep video about basics , thx

[@anonymouslyme9260]

A const reference does not necessarily turn into a pointer. Both is possible in this case: by value and reference. The compiler chooses which (certainly the optimal one) l/r value ist't relevant here

[@hashcash7340]

9:42 that's a good idea everyone will be able to watch those small videos and learn something new, like i did in this video ;)

[@sanyi_derda]

9:45 like the new idea :)

[@YoungAdventures]

I love this video format!

[@LogicEu]

Very real and useful advice going on here

[@Mozartenhimer]

I've been thinking about this a lot recently. I've been dealing with some pretty hot code with some 64 byte values, and I've been wondering how terrible just copying it is on the stack. Did some microbenchmarks this evening, and it's not bad at all.

[@gerooq]

yeah shorter more focused videos sounds like a good idea, but i gotta say i really do like this format i end up learning alot regardless

[@gerooq]

and theres room for jokes and other tidbits which honestly makes me wanna watch your videos more, cuz i mean think abuot it there are plenty of c++ videos on youtube, people watch yours because of your personality, and that doesnt just include the way you teach but also the videos are just entertaining too

[@rhoward99]

Multiple topic videos per review would be great!