golang eval 代码
文件路径：/src/go/types/eval.go
/ Copyright 2013 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 types
import (
"fmt"
"go/ast"
"go/parser"
"go/token"
)
/ Eval returns the type and, if constant, the value for the
/ expression expr, evaluated at position pos of package pkg,
/ which must have been derived from type-checking an AST with
/ complete position information relative to the provided file
/ set.
/
/ The meaning of the parameters fset, pkg, and pos is the
/ same as in CheckExpr. An error is returned if expr cannot
/ be parsed successfully, or the resulting expr AST cannot be
/ type-checked.
func Eval(fset *token.FileSet, pkg *Package, pos token.Pos, expr string) (_ TypeAndValue, err error) {
/ parse expressions
node, err := parser.ParseExprFrom(fset, "eval", expr, 0)
if err != nil {
return TypeAndValue{}, err
}
info := &Info{
Types: make(map[ast.Expr]TypeAndValue),
}
err = CheckExpr(fset, pkg, pos, node, info)
return info.Types[node], err
}
/ CheckExpr type checks the expression expr as if it had appeared at position
/ pos of package pkg. Type information about the expression is recorded in
/ info. The expression may be an identifier denoting an uninstantiated generic
/ function or type.
/
/ If pkg == nil, the Universe scope is used and the provided
/ position pos is ignored. If pkg != nil, and pos is invalid,
/ the package scope is used. Otherwise, pos must belong to the
/ package.
/
/ An error is returned if pos is not within the package or
/ if the node cannot be type-checked.
/
/ Note: Eval and CheckExpr should not be used instead of running Check
/ to compute types and values, but in addition to Check, as these
/ functions ignore the context in which an expression is used (e.g., an
/ assignment). Thus, top-level untyped constants will return an
/ untyped type rather then the respective context-specific type.
func CheckExpr(fset *token.FileSet, pkg *Package, pos token.Pos, expr ast.Expr, info *Info) (err error) {
/ determine scope
var scope *Scope
if pkg == nil {
scope = Universe
pos = token.NoPos
} else if !pos.IsValid() {
scope = pkg.scope
} else {
/ The package scope extent (position information) may be
/ incorrect (files spread across a wide range of fset
/ positions) - ignore it and just consider its children
/ (file scopes).
for _, fscope := range pkg.scope.children {
if scope = fscope.Innermost(pos); scope != nil {
break
}
}
if scope == nil || debug {
s := scope
for s != nil && s != pkg.scope {
s = s.parent
}
/ s == nil || s == pkg.scope
if s == nil {
return fmt.Errorf("no position %s found in package %s", fset.Position(pos), pkg.name)
}
}
}
/ initialize checker
check := NewChecker(nil, fset, pkg, info)
check.scope = scope
check.pos = pos
defer check.handleBailout(&err)
/ evaluate node
var x operand
check.rawExpr(&x, expr, nil, true) / allow generic expressions
check.processDelayed(0) / incl. all functions
check.recordUntyped()
return nil
}