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// Copyright 2009 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 package illustrates how basic try-catch exception handling
// can be emulated using goroutines, channels, and closures.
//
// This package is *not* intended as a general exception handler
// library.
//
package exception
import (
"fmt";
"runtime";
)
// A Handler function handles an arbitrary exception value x.
type Handler func(x interface{})
// An Exception carries an exception value.
type Exception struct {
Value interface{}; // Value may be the nil exception
}
// Try invokes a function f with a Handler to throw exceptions.
// The function f may terminate abnormally with an arbitrary
// exception x by calling throw(x) within f. If an exception is
// thrown, Try returns an *Exception; otherwise it returns nil.
//
// Usage pattern:
//
// if x := exception.Try(func(throw exception.Handler) {
// ...
// throw(42); // terminate f by throwing exception 42
// ...
// }); x != nil {
// // catch exception, e.g. print it
// fmt.Println(x.Value);
// }
//
// Alternative:
//
// exception.Try(func(throw exception.Handler) {
// ...
// throw(42); // terminate f by throwing exception 42
// ...
// }).Catch(func (x interface{}) {
// // catch exception, e.g. print it
// fmt.Println(x);
// })
//
func Try(f func(throw Handler)) *Exception {
h := make(chan *Exception);
// execute try block
go func() {
f(func(x interface{}) {
h <- &Exception{x};
runtime.Goexit();
});
h <- nil; // clean termination
}();
return <-h;
}
// If x != nil, Catch invokes f with the exception value x.Value.
// See Try for usage patterns.
func (x *Exception) Catch(f Handler) {
if x != nil {
f(x.Value)
}
}
func (x *Exception) String() string {
if x != nil {
return fmt.Sprintf("exception: %v", x.Value)
}
return "";
}
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