From 07f5ab10096718a296825b3b628081559d738810 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Fri, 14 Jun 2013 18:27:35 -0700
Subject: [PATCH] Implement a deriving(Zero) attribute
---
src/libsyntax/ext/deriving/mod.rs | 2 +
src/libsyntax/ext/deriving/zero.rs | 96 ++++++++++++++++++++++++++++++
src/test/run-pass/deriving-zero.rs | 40 +++++++++++++
3 files changed, 138 insertions(+)
create mode 100644 src/libsyntax/ext/deriving/zero.rs
create mode 100644 src/test/run-pass/deriving-zero.rs
diff --git a/src/libsyntax/ext/deriving/mod.rs b/src/libsyntax/ext/deriving/mod.rs
index 606e372a25d..69069026801 100644
--- a/src/libsyntax/ext/deriving/mod.rs
+++ b/src/libsyntax/ext/deriving/mod.rs
@@ -32,6 +32,7 @@ pub mod encodable;
pub mod decodable;
pub mod rand;
pub mod to_str;
+pub mod zero;
#[path="cmp/eq.rs"]
pub mod eq;
@@ -99,6 +100,7 @@ pub fn expand_meta_deriving(cx: @ExtCtxt,
"Rand" => expand!(rand::expand_deriving_rand),
"ToStr" => expand!(to_str::expand_deriving_to_str),
+ "Zero" => expand!(zero::expand_deriving_zero),
ref tname => {
cx.span_err(titem.span, fmt!("unknown \
diff --git a/src/libsyntax/ext/deriving/zero.rs b/src/libsyntax/ext/deriving/zero.rs
new file mode 100644
index 00000000000..121d8351ee4
--- /dev/null
+++ b/src/libsyntax/ext/deriving/zero.rs
@@ -0,0 +1,96 @@
+// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use core::prelude::*;
+
+use ast::{meta_item, item, expr};
+use codemap::span;
+use ext::base::ExtCtxt;
+use ext::build::AstBuilder;
+use ext::deriving::generic::*;
+
+use core::vec;
+
+pub fn expand_deriving_zero(cx: @ExtCtxt,
+ span: span,
+ mitem: @meta_item,
+ in_items: ~[@item])
+ -> ~[@item] {
+ let trait_def = TraitDef {
+ path: Path::new(~["std", "num", "Zero"]),
+ additional_bounds: ~[],
+ generics: LifetimeBounds::empty(),
+ methods: ~[
+ MethodDef {
+ name: "zero",
+ generics: LifetimeBounds::empty(),
+ explicit_self: None,
+ args: ~[],
+ ret_ty: Self,
+ const_nonmatching: false,
+ combine_substructure: zero_substructure
+ },
+ MethodDef {
+ name: "is_zero",
+ generics: LifetimeBounds::empty(),
+ explicit_self: borrowed_explicit_self(),
+ args: ~[],
+ ret_ty: Literal(Path::new(~["bool"])),
+ const_nonmatching: false,
+ combine_substructure: |cx, span, substr| {
+ cs_and(|cx, span, _, _| cx.span_bug(span,
+ "Non-matching enum \
+ variant in \
+ deriving(Zero)"),
+ cx, span, substr)
+ }
+ }
+ ]
+ };
+ trait_def.expand(cx, span, mitem, in_items)
+}
+
+fn zero_substructure(cx: @ExtCtxt, span: span, substr: &Substructure) -> @expr {
+ let zero_ident = ~[
+ cx.ident_of("std"),
+ cx.ident_of("num"),
+ cx.ident_of("Zero"),
+ cx.ident_of("zero")
+ ];
+ let zero_call = || {
+ cx.expr_call_global(span, copy zero_ident, ~[])
+ };
+
+ return match *substr.fields {
+ StaticStruct(_, ref summary) => {
+ match *summary {
+ Left(count) => {
+ if count == 0 {
+ cx.expr_ident(span, substr.type_ident)
+ } else {
+ let exprs = vec::from_fn(count, |_| zero_call());
+ cx.expr_call_ident(span, substr.type_ident, exprs)
+ }
+ }
+ Right(ref fields) => {
+ let zero_fields = do fields.map |ident| {
+ cx.field_imm(span, *ident, zero_call())
+ };
+ cx.expr_struct_ident(span, substr.type_ident, zero_fields)
+ }
+ }
+ }
+ StaticEnum(*) => {
+ cx.span_fatal(span, "`Zero` cannot be derived for enums, \
+ only structs")
+ }
+ _ => cx.bug("Non-static method in `deriving(Zero)`")
+ };
+}
diff --git a/src/test/run-pass/deriving-zero.rs b/src/test/run-pass/deriving-zero.rs
new file mode 100644
index 00000000000..2ee57624112
--- /dev/null
+++ b/src/test/run-pass/deriving-zero.rs
@@ -0,0 +1,40 @@
+// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::util;
+use std::num::Zero;
+
+#[deriving(Zero)]
+struct A;
+#[deriving(Zero)]
+struct B(int);
+#[deriving(Zero)]
+struct C(int, int);
+#[deriving(Zero)]
+struct D { a: int }
+#[deriving(Zero)]
+struct E { a: int, b: int }
+
+#[deriving(Zero)]
+struct Lots {
+ a: ~str,
+ b: @str,
+ c: Option<util::NonCopyable>,
+ d: u8,
+ e: char,
+ f: float,
+ g: (f32, char),
+ h: ~[util::NonCopyable],
+ i: @mut (int, int),
+}
+
+fn main() {
+ assert!(Zero::zero::<Lots>().is_zero());
+}