Consider allowing limited type inference in static declarations

[rust-highfive]

Issue by sfackler
Thursday Sep 19, 2013 at 23:23 GMT

For earlier discussion, see rust-lang/rust#9346

This issue was labelled with: A-typesystem, B-RFC in the Rust repository

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Currently, statics must have a type annotation as doing global type inference to resolve the type is a bad idea. However, this leads to some annoying duplication, especially when defining a static struct instance. For example, from extra::base64:

pub static STANDARD: Config =
    Config {char_set: Standard, pad: true, line_length: None};

There's no ambiguity in the type of the RHS, but the LHS must repeat the type anyways.

Would it be possible/reasonable to infer the type of statics from the RHS of the assignment where possible? Things like this would be work:

pub static STANDARD =
    Config {char_set: Standard, pad: true, line_length: None};

pub static HELLO = "hello, world!";

pub static HELLO_BYTES = bytes!("hello, world!");

pub static BAR = 18u8;

but

pub static BAZ = 10;

would not since the type isn't specified (or maybe it would resolve to int?). Untyped integer literals and generic types containing them are actually the only things I can think of that would require a type annotation.

[Centril]

Closing in favor of #1349.