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// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use ast::{MetaItem, item, Expr};
use codemap::Span;
use ext::base::ExtCtxt;
use ext::build::AstBuilder;
use ext::deriving::generic::*;
use std::vec;
pub fn expand_deriving_default(cx: @ExtCtxt,
span: Span,
mitem: @MetaItem,
in_items: ~[@item])
-> ~[@item] {
let trait_def = TraitDef {
path: Path::new(~["std", "default", "Default"]),
additional_bounds: ~[],
generics: LifetimeBounds::empty(),
methods: ~[
MethodDef {
name: "default",
generics: LifetimeBounds::empty(),
explicit_self: None,
args: ~[],
ret_ty: Self,
const_nonmatching: false,
combine_substructure: default_substructure
},
]
};
trait_def.expand(cx, span, mitem, in_items)
}
fn default_substructure(cx: @ExtCtxt, span: Span, substr: &Substructure) -> @Expr {
let default_ident = ~[
cx.ident_of("std"),
cx.ident_of("default"),
cx.ident_of("Default"),
cx.ident_of("default")
];
let default_call = cx.expr_call_global(span, default_ident.clone(), ~[]);
return match *substr.fields {
StaticStruct(_, ref summary) => {
match *summary {
Left(count) => {
if count == 0 {
cx.expr_ident(span, substr.type_ident)
} else {
let exprs = vec::from_elem(count, default_call);
cx.expr_call_ident(span, substr.type_ident, exprs)
}
}
Right(ref fields) => {
let default_fields = do fields.map |ident| {
cx.field_imm(span, *ident, default_call)
};
cx.expr_struct_ident(span, substr.type_ident, default_fields)
}
}
}
StaticEnum(*) => {
cx.span_fatal(span, "`Default` cannot be derived for enums, \
only structs")
}
_ => cx.bug("Non-static method in `deriving(Default)`")
};
}
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