5af2978f77
git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk@12108 626c5289-ae23-0410-ae9c-e8d60b6d4f22
81 lines
2.1 KiB
HTML
81 lines
2.1 KiB
HTML
<html>
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<head>
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<title>SWIG:Examples:go:callback</title>
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</head>
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<body bgcolor="#ffffff">
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<tt>SWIG/Examples/go/callback/</tt>
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<hr>
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<H2>Implementing C++ callbacks in Go</H2>
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<p>
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This example illustrates how to use directors to implement C++
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callbacks in Go.
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</p>
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<p>
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Because Go and C++ use inheritance differently, you must call a
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different function to create a class which uses callbacks. Instead of
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calling the usual constructor function whose name is <tt>New</tt>
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followed by the capitalized name of the class, you call a function
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named <tt>NewDirector</tt> followed by the capitalized name of the
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class.
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</p>
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<p>
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The first argument to the <tt>NewDirector</tt> function is an instance
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of a type. The <tt>NewDirector</tt> function will return an interface
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value as usual. However, when calling any method on the returned
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value, the program will first check whether the value passed
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to <tt>NewDirector</tt> implements that method. If it does, the
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method will be called in Go. This is true whether the method is
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called from Go code or C++ code.
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</p>
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<p>
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Note that the Go code will be called with just the Go value, not the
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C++ value. If the Go code needs to call a C++ method on itself, you
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need to get a copy of the C++ object. This is typically done as
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follows:
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<blockquote>
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<pre>
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type Child struct { abi Parent }
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func (p *Child) ChildMethod() {
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p.abi.ParentMethod()
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}
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func f() {
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p := &Child{nil}
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d := NewDirectorParent(p)
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p.abi = d
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...
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}
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</pre>
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</blockquote>
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In other words, we first create the Go value. We pass that to
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the <tt>NewDirector</tt> function to create the C++ value; this C++
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value will be created with an association to the Go value. We then
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store the C++ value in the Go value, giving us the reverse
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association. That permits us to call parent methods from the child.
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</p>
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<p>
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To delete a director object, use the function <tt>DeleteDirector</tt>
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followed by the capitalized name of the class.
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</p>
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<p>
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<ul>
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<li><a href="example.h">example.h</a>. Header file containing some enums.
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<li><a href="example.i">example.i</a>. Interface file.
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<li><a href="runme.go">runme.go</a>. Sample Go program.
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</ul>
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<hr>
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</body>
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</html>
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