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 ext::deriving::generic::ty::*;
  17 use parse::token::InternedString;
  18 use ptr::P;
  19
  20 pub fn expand_deriving_default<F>(cx: &mut ExtCtxt,
  21                                   span: Span,
  22                                   mitem: &MetaItem,
  23                                   item: &Item,
  24                                   push: F) where
  25     F: FnOnce(P<Item>),
  26 {
  27     let inline = cx.meta_word(span, InternedString::new("inline"));
  28     let attrs = vec!(cx.attribute(span, inline));
  29     let trait_def = TraitDef {
  30         span: span,
  31         attributes: Vec::new(),
  32         path: Path::new(vec!("std", "default", "Default")),
  33         additional_bounds: Vec::new(),
  34         generics: LifetimeBounds::empty(),
  35         methods: vec!(
  36             MethodDef {
  37                 name: "default",
  38                 generics: LifetimeBounds::empty(),
  39                 explicit_self: None,
  40                 args: Vec::new(),
  41                 ret_ty: Self,
  42                 attributes: attrs,
  43                 combine_substructure: combine_substructure(box |a, b, c| {
  44                     default_substructure(a, b, c)
  45                 })
  46             })
  47     };
  48     trait_def.expand(cx, mitem, item, push)
  49 }
  50
  51 fn default_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> P<Expr> {
  52     let default_ident = vec!(
  53         cx.ident_of("std"),
  54         cx.ident_of("default"),
  55         cx.ident_of("Default"),
  56         cx.ident_of("default")
  57     );
  58     let default_call = |&: span| cx.expr_call_global(span, default_ident.clone(), Vec::new());
  59
  60     return match *substr.fields {
  61         StaticStruct(_, ref summary) => {
  62             match *summary {
  63                 Unnamed(ref fields) => {
  64                     if fields.is_empty() {
  65                         cx.expr_ident(trait_span, substr.type_ident)
  66                     } else {
  67                         let exprs = fields.iter().map(|sp| default_call(*sp)).collect();
  68                         cx.expr_call_ident(trait_span, substr.type_ident, exprs)
  69                     }
  70                 }
  71                 Named(ref fields) => {
  72                     let default_fields = fields.iter().map(|&(ident, span)| {
  73                         cx.field_imm(span, ident, default_call(span))
  74                     }).collect();
  75                     cx.expr_struct_ident(trait_span, substr.type_ident, default_fields)
  76                 }
  77             }
  78         }
  79         StaticEnum(..) => {
  80             cx.span_err(trait_span, "`Default` cannot be derived for enums, only structs");
  81             // let compilation continue
  82             cx.expr_usize(trait_span, 0)
  83         }
  84         _ => cx.span_bug(trait_span, "Non-static method in `derive(Default)`")
  85     };
  86 }