Hi there, if i write let s1: str = "hi"; compiler complains: the size for values of type str cannot be known at compilation time. OK. but 'h' + 'i' has a well defined size. So why compiler is unable to evalute the size of "hi"? Thx.

It’s a fundamental property of the str type that you can’t ever store one directly in a variable. Instead, it can only exist as part of another type, like &str, Box<str>, or (implicitly) String. The compiler error message is summarizing why str is designed this way, even though it might not be lit…

To be clear, the compiler is not trying to evaluate the size of "hi". A variable with type str needs to be able to store any possible value of that type, including strings that are two gigabytes long. Because of this, a variable cannot have the type str. In this particular case, we should add that "…

Note that the error message is (as you say): error[E0277]: the size for values of type `str` cannot be known at compilation time It says, "values of type str". It doesn't refer to the particular value "hi", but to values of str in general. When you declare a variable s1: str in your code, then th…

[image] jbe: Honestly, I'm not sure when it's best to use let and when to use const. If you're not sure you need const, that almost always means you need let. If in C you'd used #define, that means you need const (or macros).

[image] alice: If you want a variable that actually stores the string data directly, you can do this: let s1 = [b'h', b'i']; Even better, you can move out of a byte string literal to achieve the same effect in a slightly more ergonomic way: let s1 = *b"hi";

[image] jbe: Honestly, I'm not sure when it's best to use let and when to use const. It confuses me sometimes. When you use const, you will have to specify the type explicitly and you should use all uppercase letters for the name. A let binding (conceptually at least—the optimiser may cause o…

Thx you all for your answers. All this is really instructive in relation to a somewhat anomalous topic for those who come from certain other languages (me, for example)

Str size at compile time

quinedot June 15, 2022, 6:14pm 9

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Str size at compile time

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