[vlovich123]

Every new standard incorporates language & library changes. A perfect example of this is r-value references. That was a new language feature in C++11 & was adopted by all the standard library containers & algorithms.

Not sure which part of std::string you're referring to but the compiler generally doesn't contain any knowledge of the library itself. It does goes the other way though where the standard library has to know how to implement certain functionality on a given compiler (some type traits functionality IIRC isn't possible to implement without compiler builtins that expose the AST to you). I think Rust has taken a more sustainable approach with their macro system which can modify the AST instead of relying on builtins but even in Rust I suspect they use builtins in certain places of their standard library.

Today's STL implementations are going to be better performing and more robust than anything you'd write yourself so generally a good idea to stick to it as a rule of thumb for the majority of code.

[atq2119]

> even in Rust I suspect they use builtins in certain places of their standard library.

There are places in the rust standard library which just omit the implementation because it's magically filled in by the compiler based on the type and function names. Which, for really low-level and fundamental functionality, seems fair game to me.

[gpderetta]

As non exhaustive list, compilers have have intimate knowledge of:

* various operator new * all the type traits * a lot of the names inherited from the C library

compilers could do much more, but in general they prefer to implement generic optimizations instead of targeting a specific library name (for example removing allocation for stack allocated std::strings was not done until the generic removal of alloc/free was implemented).

[MaxBarraclough]

Many of the type-traits can be implemented without specific compiler support. That's how Boost managed it. Here's their implementation of is_signed if you're curious [0].

I believe some standard-library type-traits cannot be implemented without specific compiler support.

[0] https://github.com/boostorg/type_traits/blob/059ed883/includ...