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      1 // Copyright 2013 The Go Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 // This file implements objsets.
      6 //
      7 // An objset is similar to a Scope but objset elements
      8 // are identified by their unique id, instead of their
      9 // object name.
     10 
     11 package types
     12 
     13 // An objset is a set of objects identified by their unique id.
     14 // The zero value for objset is a ready-to-use empty objset.
     15 type objset map[string]Object // initialized lazily
     16 
     17 // insert attempts to insert an object obj into objset s.
     18 // If s already contains an alternative object alt with
     19 // the same name, insert leaves s unchanged and returns alt.
     20 // Otherwise it inserts obj and returns nil.
     21 func (s *objset) insert(obj Object) Object {
     22 	id := obj.Id()
     23 	if alt := (*s)[id]; alt != nil {
     24 		return alt
     25 	}
     26 	if *s == nil {
     27 		*s = make(map[string]Object)
     28 	}
     29 	(*s)[id] = obj
     30 	return nil
     31 }
     32