src/libsyntax/ext/deriving/zero.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_zero(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", "num", "Zero")),
  29         additional_bounds: Vec::new(),
  30         generics: LifetimeBounds::empty(),
  31         methods: vec!(
  32             MethodDef {
  33                 name: "zero",
  34                 generics: LifetimeBounds::empty(),
  35                 explicit_self: None,
  36                 args: Vec::new(),
  37                 ret_ty: Self,
  38                 attributes: attrs.clone(),
  39                 const_nonmatching: false,
  40                 combine_substructure: combine_substructure(|a, b, c| {
  41                     zero_substructure(a, b, c)
  42                 })
  43             },
  44             MethodDef {
  45                 name: "is_zero",
  46                 generics: LifetimeBounds::empty(),
  47                 explicit_self: borrowed_explicit_self(),
  48                 args: Vec::new(),
  49                 ret_ty: Literal(Path::new(vec!("bool"))),
  50                 attributes: attrs,
  51                 const_nonmatching: false,
  52                 combine_substructure: combine_substructure(|cx, span, substr| {
  53                     cs_and(|cx, span, _, _| cx.span_bug(span,
  54                                                         "Non-matching enum \
  55                                                          variant in \
  56                                                          deriving(Zero)"),
  57                            cx, span, substr)
  58                 })
  59             }
  60         )
  61     };
  62     trait_def.expand(cx, mitem, item, push)
  63 }
  64
  65 fn zero_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> @Expr {
  66     let zero_ident = vec!(
  67         cx.ident_of("std"),
  68         cx.ident_of("num"),
  69         cx.ident_of("Zero"),
  70         cx.ident_of("zero")
  71     );
  72     let zero_call = |span| cx.expr_call_global(span, zero_ident.clone(), Vec::new());
  73
  74     return match *substr.fields {
  75         StaticStruct(_, ref summary) => {
  76             match *summary {
  77                 Unnamed(ref fields) => {
  78                     if fields.is_empty() {
  79                         cx.expr_ident(trait_span, substr.type_ident)
  80                     } else {
  81                         let exprs = fields.iter().map(|sp| zero_call(*sp)).collect();
  82                         cx.expr_call_ident(trait_span, substr.type_ident, exprs)
  83                     }
  84                 }
  85                 Named(ref fields) => {
  86                     let zero_fields = fields.iter().map(|&(ident, span)| {
  87                         cx.field_imm(span, ident, zero_call(span))
  88                     }).collect();
  89                     cx.expr_struct_ident(trait_span, substr.type_ident, zero_fields)
  90                 }
  91             }
  92         }
  93         StaticEnum(..) => {
  94             cx.span_err(trait_span, "`Zero` cannot be derived for enums, only structs");
  95             // let compilation continue
  96             cx.expr_uint(trait_span, 0)
  97         }
  98         _ => cx.bug("Non-static method in `deriving(Zero)`")
  99     };
 100 }