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What you seem to be describing is "unspecified behaviour" or "implementation defined behaviour". If your program contains undefined behaviour the compiler make

What you seem to be describing is "unspecified behaviour" or "implementation defined behaviour". If your program contains undefined behaviour the compiler makes no guarantees about how your program will behave. For more see: https://blog.regehr.org/archives/213 https://blog.regehr.org/archives/213 and https://raphlinus.github.io/programming/rust/2018/08/17/undefined-behavior.html https://raphlinus.github.io/programming/rust/2018/08/17/unde... .

nwmcsween 6y ago
If there is one implementation as the definition then by default all behaviour is defined by the implementation, and hence parent is correct.
- wmanley 5y ago
  No. If we accept your argument then this would be correct: > In absence of a standard effectively every language construct is 'implementation defined behaviour'. But the parent said: > In absence of a standard effectively every language construct is 'undefined behavior'. Undefined behaviour != implementation defined behaviour. Both of these things exist in C and are separate. You can rely on implementation defined behaviour giving some consistent result on a given, compiler and hardware. You cannot rely on the behaviour of your program if you hit undefined behaviour.
  - nwmcsween 5y ago
    I didn't state 'implementation defined behavior' which encompasses more than the Rust implementation. The Rust implementation defines the behavior, for example signed int overflow.
    - roca 5y ago
      The "Rust Book" says signed integer overflow to be two's complement in release builds and panic in debug builds: https://doc.rust-lang.org/book/ch03-02-data-types.html https://doc.rust-lang.org/book/ch03-02-data-types.html That's clear enough for programmers to rely on. It is nonsense to argue that this is equivalent to C's "the compiler may do anything it wants" just because the "Rust Book" is not called the "Rust Standard" or not "formal" enough.

nwmcsween 6y ago

If there is one implementation as the definition then by default all behaviour is defined by the implementation, and hence parent is correct.

wmanley 5y ago
No. If we accept your argument then this would be correct: > In absence of a standard effectively every language construct is 'implementation defined behaviour'. But the parent said: > In absence of a standard effectively every language construct is 'undefined behavior'. Undefined behaviour != implementation defined behaviour. Both of these things exist in C and are separate. You can rely on implementation defined behaviour giving some consistent result on a given, compiler and hardware. You cannot rely on the behaviour of your program if you hit undefined behaviour.
- nwmcsween 5y ago
  I didn't state 'implementation defined behavior' which encompasses more than the Rust implementation. The Rust implementation defines the behavior, for example signed int overflow.
  - roca 5y ago
    The "Rust Book" says signed integer overflow to be two's complement in release builds and panic in debug builds: https://doc.rust-lang.org/book/ch03-02-data-types.html https://doc.rust-lang.org/book/ch03-02-data-types.html That's clear enough for programmers to rely on. It is nonsense to argue that this is equivalent to C's "the compiler may do anything it wants" just because the "Rust Book" is not called the "Rust Standard" or not "formal" enough.