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
  17 pub fn expand_deriving_zero(cx: &mut ExtCtxt,
  18                             span: Span,
  19                             mitem: @MetaItem,
  20                             in_items: ~[@Item])
  21                             -> ~[@Item] {
  22     let trait_def = TraitDef {
  23         span: span,
  24         path: Path::new(~["std", "num", "Zero"]),
  25         additional_bounds: ~[],
  26         generics: LifetimeBounds::empty(),
  27         methods: ~[
  28             MethodDef {
  29                 name: "zero",
  30                 generics: LifetimeBounds::empty(),
  31                 explicit_self: None,
  32                 args: ~[],
  33                 ret_ty: Self,
  34                 inline: true,
  35                 const_nonmatching: false,
  36                 combine_substructure: zero_substructure
  37             },
  38             MethodDef {
  39                 name: "is_zero",
  40                 generics: LifetimeBounds::empty(),
  41                 explicit_self: borrowed_explicit_self(),
  42                 args: ~[],
  43                 ret_ty: Literal(Path::new(~["bool"])),
  44                 inline: true,
  45                 const_nonmatching: false,
  46                 combine_substructure: |cx, span, substr| {
  47                     cs_and(|cx, span, _, _| cx.span_bug(span,
  48                                                         "Non-matching enum \
  49                                                          variant in \
  50                                                          deriving(Zero)"),
  51                            cx, span, substr)
  52                 }
  53             }
  54         ]
  55     };
  56     trait_def.expand(cx, mitem, in_items)
  57 }
  58
  59 fn zero_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> @Expr {
  60     let zero_ident = ~[
  61         cx.ident_of("std"),
  62         cx.ident_of("num"),
  63         cx.ident_of("Zero"),
  64         cx.ident_of("zero")
  65     ];
  66     let zero_call = |span| cx.expr_call_global(span, zero_ident.clone(), ~[]);
  67
  68     return match *substr.fields {
  69         StaticStruct(_, ref summary) => {
  70             match *summary {
  71                 Unnamed(ref fields) => {
  72                     if fields.is_empty() {
  73                         cx.expr_ident(trait_span, substr.type_ident)
  74                     } else {
  75                         let exprs = fields.map(|sp| zero_call(*sp));
  76                         cx.expr_call_ident(trait_span, substr.type_ident, exprs)
  77                     }
  78                 }
  79                 Named(ref fields) => {
  80                     let zero_fields = fields.map(|&(ident, span)| {
  81                         cx.field_imm(span, ident, zero_call(span))
  82                     });
  83                     cx.expr_struct_ident(trait_span, substr.type_ident, zero_fields)
  84                 }
  85             }
  86         }
  87         StaticEnum(..) => {
  88             cx.span_err(trait_span, "`Zero` cannot be derived for enums, only structs");
  89             // let compilation continue
  90             cx.expr_uint(trait_span, 0)
  91         }
  92         _ => cx.bug("Non-static method in `deriving(Zero)`")
  93     };
  94 }