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Also, there are a whole host of very common types (integers, etc.) that actually want to be passed by value and copied. There's no point in making a pointer to

by wycats 12y ago

Also, there are a whole host of very common types (integers, etc.) that actually want to be passed by value and copied. There's no point in making a pointer to an integer and then dereferencing the pointer in the callee when an integer fits into the same amount of space as a pointer in the first place. Very simple types (without heap pointers or destructors) can be passed by value and efficiently copied. You end up with a bit of an intuition for "value types" (simple types whose identity is bound up in the shallow memory that they contain). In other GC'ed languages, there is a fixed set of these kinds of values (often called "primitives"). In Rust, any simple user-specified type can be a "primitive".

Animats 12y ago
If something is immutable (and doesn't own something else), it doesn't matter whether it's passed by value or reference. That's a decision the compiler can, and should, make, as an optimization decision. In Modula, where pass-as-read-only was the default, small items were passed by value and large ones by reference. "Small" is a CPU-dependent optimization and should be left to the compiler, not "user intuition". The default should be pass as read-only reference. If you want a copy of something, you should have to explicitly make one. If you want write access, you should have to say so. Rust has all the right concepts, but the defaults aren't in the safest direction. The experience of "const" in C/C++ teaches us that they should be.
- wycats 12y ago
  There is an important distinction in Rust: ownership. Copyable objects are (by definition) simple enough that copying them does not introduce aliasing. Objects with heap pointers or destructors cannot be copied, because now there would be two "owners" of those values. For what it's worth, I've found that a lot of these assumptions ("it doesn't matter, let the compile optimize it") really remove the programmer from important power. And before you find yourself saying "are you saying everyone should write everything in assembler?": 1. There is a distinction between writing code in assembler and having to use a `&` sigil for "by-reference" in a language that has lambdas, traits and many other high-level features. 2. You should generally use Rust for cases where performance characteristics are important, and where control over memory is important. If you're sure it's not important, by all means go with a higher-level language that abstracts it away. I made this point (perhaps more clearly) in my talk at GoGaRuCo: http://www.youtube.com/watch?v=ySW6Yk_DerY http://www.youtube.com/watch?v=ySW6Yk_DerY
- kibwen 12y ago
  > the defaults aren't in the safest direction Can you elaborate on this? I'm curious to know how you perceive Rust's defaults as unsafe.

by wycats 12y ago

Animats 12y ago

If something is immutable (and doesn't own something else), it doesn't matter whether it's passed by value or reference. That's a decision the compiler can, and should, make, as an optimization decision. In Modula, where pass-as-read-only was the default, small items were passed by value and large ones by reference. "Small" is a CPU-dependent optimization and should be left to the compiler, not "user intuition". The default should be pass as read-only reference. If you want a copy of something, you should have to explicitly make one. If you want write access, you should have to say so. Rust has all the right concepts, but the defaults aren't in the safest direction. The experience of "const" in C/C++ teaches us that they should be.

wycats 12y ago
There is an important distinction in Rust: ownership. Copyable objects are (by definition) simple enough that copying them does not introduce aliasing. Objects with heap pointers or destructors cannot be copied, because now there would be two "owners" of those values. For what it's worth, I've found that a lot of these assumptions ("it doesn't matter, let the compile optimize it") really remove the programmer from important power. And before you find yourself saying "are you saying everyone should write everything in assembler?": 1. There is a distinction between writing code in assembler and having to use a `&` sigil for "by-reference" in a language that has lambdas, traits and many other high-level features. 2. You should generally use Rust for cases where performance characteristics are important, and where control over memory is important. If you're sure it's not important, by all means go with a higher-level language that abstracts it away. I made this point (perhaps more clearly) in my talk at GoGaRuCo: http://www.youtube.com/watch?v=ySW6Yk_DerY http://www.youtube.com/watch?v=ySW6Yk_DerY
kibwen 12y ago
> the defaults aren't in the safest direction Can you elaborate on this? I'm curious to know how you perceive Rust's defaults as unsafe.