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Source file src/go/types/ordering.go

Documentation: go/types

  // Copyright 2014 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.
  
  // This file implements resolveOrder.
  
  package types
  
  import (
  	"go/ast"
  	"sort"
  )
  
  // resolveOrder computes the order in which package-level objects
  // must be type-checked.
  //
  // Interface types appear first in the list, sorted topologically
  // by dependencies on embedded interfaces that are also declared
  // in this package, followed by all other objects sorted in source
  // order.
  //
  // TODO(gri) Consider sorting all types by dependencies here, and
  // in the process check _and_ report type cycles. This may simplify
  // the full type-checking phase.
  //
  func (check *Checker) resolveOrder() []Object {
  	var ifaces, others []Object
  
  	// collect interface types with their dependencies, and all other objects
  	for obj := range check.objMap {
  		if ityp := check.interfaceFor(obj); ityp != nil {
  			ifaces = append(ifaces, obj)
  			// determine dependencies on embedded interfaces
  			for _, f := range ityp.Methods.List {
  				if len(f.Names) == 0 {
  					// Embedded interface: The type must be a (possibly
  					// qualified) identifier denoting another interface.
  					// Imported interfaces are already fully resolved,
  					// so we can ignore qualified identifiers.
  					if ident, _ := f.Type.(*ast.Ident); ident != nil {
  						embedded := check.pkg.scope.Lookup(ident.Name)
  						if check.interfaceFor(embedded) != nil {
  							check.objMap[obj].addDep(embedded)
  						}
  					}
  				}
  			}
  		} else {
  			others = append(others, obj)
  		}
  	}
  
  	// final object order
  	var order []Object
  
  	// sort interface types topologically by dependencies,
  	// and in source order if there are no dependencies
  	sort.Sort(inSourceOrder(ifaces))
  	visited := make(objSet)
  	for _, obj := range ifaces {
  		check.appendInPostOrder(&order, obj, visited)
  	}
  
  	// sort everything else in source order
  	sort.Sort(inSourceOrder(others))
  
  	return append(order, others...)
  }
  
  // interfaceFor returns the AST interface denoted by obj, or nil.
  func (check *Checker) interfaceFor(obj Object) *ast.InterfaceType {
  	tname, _ := obj.(*TypeName)
  	if tname == nil {
  		return nil // not a type
  	}
  	d := check.objMap[obj]
  	if d == nil {
  		check.dump("%s: %s should have been declared", obj.Pos(), obj.Name())
  		unreachable()
  	}
  	if d.typ == nil {
  		return nil // invalid AST - ignore (will be handled later)
  	}
  	ityp, _ := d.typ.(*ast.InterfaceType)
  	return ityp
  }
  
  func (check *Checker) appendInPostOrder(order *[]Object, obj Object, visited objSet) {
  	if visited[obj] {
  		// We've already seen this object; either because it's
  		// already added to order, or because we have a cycle.
  		// In both cases we stop. Cycle errors are reported
  		// when type-checking types.
  		return
  	}
  	visited[obj] = true
  
  	d := check.objMap[obj]
  	for _, obj := range orderedSetObjects(d.deps) {
  		check.appendInPostOrder(order, obj, visited)
  	}
  
  	*order = append(*order, obj)
  }
  
  func orderedSetObjects(set objSet) []Object {
  	list := make([]Object, len(set))
  	i := 0
  	for obj := range set {
  		// we don't care about the map element value
  		list[i] = obj
  		i++
  	}
  	sort.Sort(inSourceOrder(list))
  	return list
  }
  
  // inSourceOrder implements the sort.Sort interface.
  type inSourceOrder []Object
  
  func (a inSourceOrder) Len() int           { return len(a) }
  func (a inSourceOrder) Less(i, j int) bool { return a[i].order() < a[j].order() }
  func (a inSourceOrder) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
  

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