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