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// 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.
/*!
The compiler code necessary to implement the #[deriving(Encodable)]
(and Decodable, in decodable.rs) extension. The idea here is that
type-defining items may be tagged with #[deriving(Encodable,
Decodable)].
For example, a type like:
#[deriving(Encodable, Decodable)]
struct Node {id: uint}
would generate two implementations like:
impl<S:extra::serialize::Encoder> Encodable<S> for Node {
fn encode(&self, s: &S) {
do s.emit_struct("Node", 1) {
s.emit_field("id", 0, || s.emit_uint(self.id))
}
}
}
impl<D:Decoder> Decodable for node_id {
fn decode(d: &D) -> Node {
do d.read_struct("Node", 1) {
Node {
id: d.read_field(~"x", 0, || decode(d))
}
}
}
}
Other interesting scenarios are whe the item has type parameters or
references other non-built-in types. A type definition like:
#[deriving(Encodable, Decodable)]
struct spanned<T> {node: T, span: Span}
would yield functions like:
impl<
S: Encoder,
T: Encodable<S>
> spanned<T>: Encodable<S> {
fn encode<S:Encoder>(s: &S) {
do s.emit_rec {
s.emit_field("node", 0, || self.node.encode(s));
s.emit_field("span", 1, || self.span.encode(s));
}
}
}
impl<
D: Decoder,
T: Decodable<D>
> spanned<T>: Decodable<D> {
fn decode(d: &D) -> spanned<T> {
do d.read_rec {
{
node: d.read_field(~"node", 0, || decode(d)),
span: d.read_field(~"span", 1, || decode(d)),
}
}
}
}
*/
use ast::{MetaItem, item, Expr, MutImmutable, MutMutable};
use codemap::Span;
use ext::base::ExtCtxt;
use ext::build::AstBuilder;
use ext::deriving::generic::*;
pub fn expand_deriving_encodable(cx: @ExtCtxt,
span: Span,
mitem: @MetaItem,
in_items: ~[@item]) -> ~[@item] {
let trait_def = TraitDef {
path: Path::new_(~["extra", "serialize", "Encodable"], None,
~[~Literal(Path::new_local("__E"))], true),
additional_bounds: ~[],
generics: LifetimeBounds {
lifetimes: ~[],
bounds: ~[("__E", ~[Path::new(~["extra", "serialize", "Encoder"])])],
},
methods: ~[
MethodDef {
name: "encode",
generics: LifetimeBounds::empty(),
explicit_self: Some(Some(Borrowed(None, MutImmutable))),
args: ~[Ptr(~Literal(Path::new_local("__E")),
Borrowed(None, MutMutable))],
ret_ty: nil_ty(),
const_nonmatching: true,
combine_substructure: encodable_substructure,
},
]
};
trait_def.expand(cx, span, mitem, in_items)
}
fn encodable_substructure(cx: @ExtCtxt, span: Span,
substr: &Substructure) -> @Expr {
let encoder = substr.nonself_args[0];
// throw an underscore in front to suppress unused variable warnings
let blkarg = cx.ident_of("_e");
let blkencoder = cx.expr_ident(span, blkarg);
let encode = cx.ident_of("encode");
return match *substr.fields {
Struct(ref fields) => {
let emit_struct_field = cx.ident_of("emit_struct_field");
let mut stmts = ~[];
for (i, f) in fields.iter().enumerate() {
let (name, val) = match *f {
(Some(id), e, _) => (cx.str_of(id), e),
(None, e, _) => (fmt!("_field%u", i).to_managed(), e)
};
let enc = cx.expr_method_call(span, val, encode, ~[blkencoder]);
let lambda = cx.lambda_expr_1(span, enc, blkarg);
let call = cx.expr_method_call(span, blkencoder,
emit_struct_field,
~[cx.expr_str(span, name),
cx.expr_uint(span, i),
lambda]);
stmts.push(cx.stmt_expr(call));
}
let blk = cx.lambda_stmts_1(span, stmts, blkarg);
cx.expr_method_call(span, encoder, cx.ident_of("emit_struct"),
~[cx.expr_str(span, cx.str_of(substr.type_ident)),
cx.expr_uint(span, fields.len()),
blk])
}
EnumMatching(idx, variant, ref fields) => {
// We're not generating an AST that the borrow checker is expecting,
// so we need to generate a unique local variable to take the
// mutable loan out on, otherwise we get conflicts which don't
// actually exist.
let me = cx.stmt_let(span, false, blkarg, encoder);
let encoder = cx.expr_ident(span, blkarg);
let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
let mut stmts = ~[];
for (i, f) in fields.iter().enumerate() {
let val = match *f { (_, e, _) => e };
let enc = cx.expr_method_call(span, val, encode, ~[blkencoder]);
let lambda = cx.lambda_expr_1(span, enc, blkarg);
let call = cx.expr_method_call(span, blkencoder,
emit_variant_arg,
~[cx.expr_uint(span, i),
lambda]);
stmts.push(cx.stmt_expr(call));
}
let blk = cx.lambda_stmts_1(span, stmts, blkarg);
let name = cx.expr_str(span, cx.str_of(variant.node.name));
let call = cx.expr_method_call(span, blkencoder,
cx.ident_of("emit_enum_variant"),
~[name,
cx.expr_uint(span, idx),
cx.expr_uint(span, fields.len()),
blk]);
let blk = cx.lambda_expr_1(span, call, blkarg);
let ret = cx.expr_method_call(span, encoder,
cx.ident_of("emit_enum"),
~[cx.expr_str(span,
cx.str_of(substr.type_ident)),
blk]);
cx.expr_block(cx.block(span, ~[me], Some(ret)))
}
_ => cx.bug("expected Struct or EnumMatching in deriving(Encodable)")
};
}
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