src/libsyntax/ext/deriving/default.rs

   1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use ast::{MetaItem, Item, Expr};
  12 use codemap::Span;
  13 use ext::base::ExtCtxt;
  14 use ext::build::AstBuilder;
  15 use ext::deriving::generic::*;
  16
  17 pub fn expand_deriving_default(cx: &mut ExtCtxt,
  18                             span: Span,
  19                             mitem: @MetaItem,
  20                             item: @Item,
  21                             push: |@Item|) {
  22     let trait_def = TraitDef {
  23         span: span,
  24         attributes: Vec::new(),
  25         path: Path::new(vec!("std", "default", "Default")),
  26         additional_bounds: Vec::new(),
  27         generics: LifetimeBounds::empty(),
  28         methods: vec!(
  29             MethodDef {
  30                 name: "default",
  31                 generics: LifetimeBounds::empty(),
  32                 explicit_self: None,
  33                 args: Vec::new(),
  34                 ret_ty: Self,
  35                 inline: true,
  36                 const_nonmatching: false,
  37                 combine_substructure: combine_substructure(|a, b, c| {
  38                     default_substructure(a, b, c)
  39                 })
  40             })
  41     };
  42     trait_def.expand(cx, mitem, item, push)
  43 }
  44
  45 fn default_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> @Expr {
  46     let default_ident = vec!(
  47         cx.ident_of("std"),
  48         cx.ident_of("default"),
  49         cx.ident_of("Default"),
  50         cx.ident_of("default")
  51     );
  52     let default_call = |span| cx.expr_call_global(span, default_ident.clone(), Vec::new());
  53
  54     return match *substr.fields {
  55         StaticStruct(_, ref summary) => {
  56             match *summary {
  57                 Unnamed(ref fields) => {
  58                     if fields.is_empty() {
  59                         cx.expr_ident(trait_span, substr.type_ident)
  60                     } else {
  61                         let exprs = fields.iter().map(|sp| default_call(*sp)).collect();
  62                         cx.expr_call_ident(trait_span, substr.type_ident, exprs)
  63                     }
  64                 }
  65                 Named(ref fields) => {
  66                     let default_fields = fields.iter().map(|&(ident, span)| {
  67                         cx.field_imm(span, ident, default_call(span))
  68                     }).collect();
  69                     cx.expr_struct_ident(trait_span, substr.type_ident, default_fields)
  70                 }
  71             }
  72         }
  73         StaticEnum(..) => {
  74             cx.span_err(trait_span, "`Default` cannot be derived for enums, only structs");
  75             // let compilation continue
  76             cx.expr_uint(trait_span, 0)
  77         }
  78         _ => cx.span_bug(trait_span, "Non-static method in `deriving(Default)`")
  79     };
  80 }