LYR-SEM0065

an attribute that cannot stand here

error · spec 11-metaprogramming

An @Name names something that is not a struct, names a generic struct, or names a struct whose markers do not admit the declaration it sits on.

Explanation

An attribute is a non-generic struct that declares a marker of std.core saying where it may stand: OnFunction, OnField, OnType, or a wider one such as OnDecl or OnAny. The marker keeps metadata from landing on declarations nobody reads it from.

Declare the struct with the marker for this site, or move the attribute to a declaration its marker admits.

Wrong

import std.core { OnField };

struct Width :: [OnField] {
    value: int,
}

@Width { value = 3 }
fn f(): void {
}

fn main(): void {
    f();
}

Right

import std.core { OnFunction };

struct Width :: [OnFunction] {
    value: int,
}

@Width { value = 3 }
fn f(): void {
}

fn main(): void {
    f();
}