CODEWITHSUNDEEP
rust
Roby Cigar
Roby Cigar

Reputation: 948

What is suffix annotation in rust?

I read this docs and stumbled on this line.

let an_integer = 5i32; // Suffix annotation

What is this mean? I am assuming that it have 5 as value and i32 as integer type. Is that correct?

Upvotes: 3

Views: 1196

Answers (1)

bk2204
bk2204

Reputation: 76629

Yes, that's correct. When you write the literal 5 in a program, it could be interpreted as a variety of types. (A literal is a value, such as 5, which is written directly into the source code instead of being computed.) If we want to express that a literal is of a certain type, we can append ("suffix") the type to it to make it explicit, as in 5i32.

This is only done with certain built-in types, such as integers and floating-point numbers, but it can come in handy in some cases. For example, the following is not valid:

fn main() {
    println!("{}", 1 << 32);
}

That's because if you specify no type at all for an integer, it defaults to i32. Since it's not valid to shift a 32-bit integer by 32 bits, Rust produces an error.

However, we can write this and it will work:

fn main() {
    println!("{}", 1u64 << 32);
}

That's because now the integer is a u64 and it's in range.

Upvotes: 10

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