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 attr;
  13 use codemap::Span;
  14 use ext::base::ExtCtxt;
  15 use ext::build::AstBuilder;
  16 use ext::deriving::generic::*;
  17 use parse::token::InternedString;
  18
  19 pub fn expand_deriving_default(cx: &mut ExtCtxt,
  20                             span: Span,
  21                             mitem: @MetaItem,
  22                             item: @Item,
  23                             push: |@Item|) {
  24     let inline = cx.meta_word(span, InternedString::new("inline"));
  25     let attrs = vec!(cx.attribute(attr::mk_attr_id(), span, inline));
  26     let trait_def = TraitDef {
  27         span: span,
  28         attributes: Vec::new(),
  29         path: Path::new(vec!("std", "default", "Default")),
  30         additional_bounds: Vec::new(),
  31         generics: LifetimeBounds::empty(),
  32         methods: vec!(
  33             MethodDef {
  34                 name: "default",
  35                 generics: LifetimeBounds::empty(),
  36                 explicit_self: None,
  37                 args: Vec::new(),
  38                 ret_ty: Self,
  39                 attributes: attrs,
  40                 const_nonmatching: false,
  41                 combine_substructure: combine_substructure(|a, b, c| {
  42                     default_substructure(a, b, c)
  43                 })
  44             })
  45     };
  46     trait_def.expand(cx, mitem, item, push)
  47 }
  48
  49 fn default_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> @Expr {
  50     let default_ident = vec!(
  51         cx.ident_of("std"),
  52         cx.ident_of("default"),
  53         cx.ident_of("Default"),
  54         cx.ident_of("default")
  55     );
  56     let default_call = |span| cx.expr_call_global(span, default_ident.clone(), Vec::new());
  57
  58     return match *substr.fields {
  59         StaticStruct(_, ref summary) => {
  60             match *summary {
  61                 Unnamed(ref fields) => {
  62                     if fields.is_empty() {
  63                         cx.expr_ident(trait_span, substr.type_ident)
  64                     } else {
  65                         let exprs = fields.iter().map(|sp| default_call(*sp)).collect();
  66                         cx.expr_call_ident(trait_span, substr.type_ident, exprs)
  67                     }
  68                 }
  69                 Named(ref fields) => {
  70                     let default_fields = fields.iter().map(|&(ident, span)| {
  71                         cx.field_imm(span, ident, default_call(span))
  72                     }).collect();
  73                     cx.expr_struct_ident(trait_span, substr.type_ident, default_fields)
  74                 }
  75             }
  76         }
  77         StaticEnum(..) => {
  78             cx.span_err(trait_span, "`Default` cannot be derived for enums, only structs");
  79             // let compilation continue
  80             cx.expr_uint(trait_span, 0)
  81         }
  82         _ => cx.span_bug(trait_span, "Non-static method in `deriving(Default)`")
  83     };
  84 }