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 use parse::token::InternedString;
  17
  18 pub fn expand_deriving_default(cx: &mut ExtCtxt,
  19                             span: Span,
  20                             mitem: @MetaItem,
  21                             item: @Item,
  22                             push: |@Item|) {
  23     let inline = cx.meta_word(span, InternedString::new("inline"));
  24     let attrs = vec!(cx.attribute(span, inline));
  25     let trait_def = TraitDef {
  26         span: span,
  27         attributes: Vec::new(),
  28         path: Path::new(vec!("std", "default", "Default")),
  29         additional_bounds: Vec::new(),
  30         generics: LifetimeBounds::empty(),
  31         methods: vec!(
  32             MethodDef {
  33                 name: "default",
  34                 generics: LifetimeBounds::empty(),
  35                 explicit_self: None,
  36                 args: Vec::new(),
  37                 ret_ty: Self,
  38                 attributes: attrs,
  39                 const_nonmatching: false,
  40                 combine_substructure: default_substructure
  41             })
  42     };
  43     trait_def.expand(cx, mitem, item, push)
  44 }
  45
  46 fn default_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> @Expr {
  47     let default_ident = vec!(
  48         cx.ident_of("std"),
  49         cx.ident_of("default"),
  50         cx.ident_of("Default"),
  51         cx.ident_of("default")
  52     );
  53     let default_call = |span| cx.expr_call_global(span, default_ident.clone(), Vec::new());
  54
  55     return match *substr.fields {
  56         StaticStruct(_, ref summary) => {
  57             match *summary {
  58                 Unnamed(ref fields) => {
  59                     if fields.is_empty() {
  60                         cx.expr_ident(trait_span, substr.type_ident)
  61                     } else {
  62                         let exprs = fields.iter().map(|sp| default_call(*sp)).collect();
  63                         cx.expr_call_ident(trait_span, substr.type_ident, exprs)
  64                     }
  65                 }
  66                 Named(ref fields) => {
  67                     let default_fields = fields.iter().map(|&(ident, span)| {
  68                         cx.field_imm(span, ident, default_call(span))
  69                     }).collect();
  70                     cx.expr_struct_ident(trait_span, substr.type_ident, default_fields)
  71                 }
  72             }
  73         }
  74         StaticEnum(..) => {
  75             cx.span_err(trait_span, "`Default` cannot be derived for enums, only structs");
  76             // let compilation continue
  77             cx.expr_uint(trait_span, 0)
  78         }
  79         _ => cx.span_bug(trait_span, "Non-static method in `deriving(Default)`")
  80     };
  81 }