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         cx: cx, span: span,
  24
  25         path: Path::new(~["std", "num", "Zero"]),
  26         additional_bounds: ~[],
  27         generics: LifetimeBounds::empty(),
  28         methods: ~[
  29             MethodDef {
  30                 name: "zero",
  31                 generics: LifetimeBounds::empty(),
  32                 explicit_self: None,
  33                 args: ~[],
  34                 ret_ty: Self,
  35                 inline: true,
  36                 const_nonmatching: false,
  37                 combine_substructure: zero_substructure
  38             },
  39             MethodDef {
  40                 name: "is_zero",
  41                 generics: LifetimeBounds::empty(),
  42                 explicit_self: borrowed_explicit_self(),
  43                 args: ~[],
  44                 ret_ty: Literal(Path::new(~["bool"])),
  45                 inline: true,
  46                 const_nonmatching: false,
  47                 combine_substructure: |cx, span, substr| {
  48                     cs_and(|cx, span, _, _| cx.span_bug(span,
  49                                                         "Non-matching enum \
  50                                                          variant in \
  51                                                          deriving(Zero)"),
  52                            cx, span, substr)
  53                 }
  54             }
  55         ]
  56     };
  57     trait_def.expand(mitem, in_items)
  58 }
  59
  60 fn zero_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> @Expr {
  61     let zero_ident = ~[
  62         cx.ident_of("std"),
  63         cx.ident_of("num"),
  64         cx.ident_of("Zero"),
  65         cx.ident_of("zero")
  66     ];
  67     let zero_call = |span| cx.expr_call_global(span, zero_ident.clone(), ~[]);
  68
  69     return match *substr.fields {
  70         StaticStruct(_, ref summary) => {
  71             match *summary {
  72                 Unnamed(ref fields) => {
  73                     if fields.is_empty() {
  74                         cx.expr_ident(trait_span, substr.type_ident)
  75                     } else {
  76                         let exprs = fields.map(|sp| zero_call(*sp));
  77                         cx.expr_call_ident(trait_span, substr.type_ident, exprs)
  78                     }
  79                 }
  80                 Named(ref fields) => {
  81                     let zero_fields = fields.map(|&(ident, span)| {
  82                         cx.field_imm(span, ident, zero_call(span))
  83                     });
  84                     cx.expr_struct_ident(trait_span, substr.type_ident, zero_fields)
  85                 }
  86             }
  87         }
  88         StaticEnum(..) => {
  89             cx.span_err(trait_span, "`Zero` cannot be derived for enums, only structs");
  90             // let compilation continue
  91             cx.expr_uint(trait_span, 0)
  92         }
  93         _ => cx.bug("Non-static method in `deriving(Zero)`")
  94     };
  95 }