I just started to play around with Rust. Trying to run the code snippet below will result in a compile time error with the message: type ascription is experimental.
use std::env;
fn main() {
let arguments: Args = env:args();
}
The docs for env:args shows that the function returns an Args struct and the Variable Binding section shows that I can set type of the variables with let varname: type = value. How I can properly assign a return value of a function to a variable?
You're looking for
let arguments: Args = env::args();
Using a single colon in an expression is type ascription, and currently you can only specify types on variable bindings. Note that the : Args annotation on this line is optional.
Using two colons allows you to access items within a namespace, so one wants env::args, not env:args.
:: to access functions in a namespace. But I don't exactly understand the reason of using :. I googled type ascription and I roughly understand what it means, but could you provide some example here to show what would be the purpose of using one semicolon in Rust?
default::Default::<String>()?::<String> specifies the template parameters of Default::default, whereas : Default specifies the return type. In this trivial case those happen to be one and the same, but that's not always the case. Type ascription also looks nicer, IMO.