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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"go/ast"
"go/token"
"reflect"
)
type simplifier struct{}
func (s *simplifier) Visit(node ast.Node) ast.Visitor {
switch n := node.(type) {
case *ast.CompositeLit:
// array, slice, and map composite literals may be simplified
outer := n
var eltType ast.Expr
switch typ := outer.Type.(type) {
case *ast.ArrayType:
eltType = typ.Elt
case *ast.MapType:
eltType = typ.Value
}
if eltType != nil {
typ := reflect.ValueOf(eltType)
for i, x := range outer.Elts {
px := &outer.Elts[i]
// look at value of indexed/named elements
if t, ok := x.(*ast.KeyValueExpr); ok {
x = t.Value
px = &t.Value
}
simplify(x)
// if the element is a composite literal and its literal type
// matches the outer literal's element type exactly, the inner
// literal type may be omitted
if inner, ok := x.(*ast.CompositeLit); ok {
if match(nil, typ, reflect.ValueOf(inner.Type)) {
inner.Type = nil
}
}
// if the outer literal's element type is a pointer type *T
// and the element is & of a composite literal of type T,
// the inner &T may be omitted.
if ptr, ok := eltType.(*ast.StarExpr); ok {
if addr, ok := x.(*ast.UnaryExpr); ok && addr.Op == token.AND {
if inner, ok := addr.X.(*ast.CompositeLit); ok {
if match(nil, reflect.ValueOf(ptr.X), reflect.ValueOf(inner.Type)) {
inner.Type = nil // drop T
*px = inner // drop &
}
}
}
}
}
// node was simplified - stop walk (there are no subnodes to simplify)
return nil
}
case *ast.RangeStmt:
// range of the form: for x, _ = range v {...}
// can be simplified to: for x = range v {...}
if n.Value != nil {
if ident, ok := n.Value.(*ast.Ident); ok && ident.Name == "_" {
n.Value = nil
}
}
}
return s
}
func simplify(node ast.Node) {
var s simplifier
ast.Walk(&s, node)
}
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