pjs/xpcom/ds/nsXPIDLString.h

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
*
* The contents of this file are subject to the Netscape Public License
* Version 1.0 (the "NPL"); you may not use this file except in
* compliance with the NPL. You may obtain a copy of the NPL at
* http://www.mozilla.org/NPL/
*
* Software distributed under the NPL is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
* for the specific language governing rights and limitations under the
* NPL.
*
* The Initial Developer of this code under the NPL is Netscape
* Communications Corporation. Portions created by Netscape are
* Copyright (C) 1998 Netscape Communications Corporation. All Rights
* Reserved.
*/
/*
A set of string wrapper classes that ease transition to use of XPIDL
interfaces. nsXPIDLString and nsXPIDLCString are to XPIDL `wstring'
and `string' out params as nsCOMPtr is to generic XPCOM interface
pointers. They help you deal with object ownership.
Consider the following interface:
interface nsIFoo {
attribute string Bar;
};
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This will generate the following C++ header file:
class nsIFoo {
NS_IMETHOD SetBar(const PRUnichar* aValue);
NS_IMETHOD GetBar(PRUnichar* *aValue);
};
The GetBar() method will allocate a copy of the nsIFoo object's
"bar" attribute, and leave you to deal with freeing it:
nsIFoo* aFoo; // assume we get this somehow
PRUnichar* bar;
aFoo->GetFoo(&bar);
// Use bar here...
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printf("bar is %s!\n", bar);
delete[] bar;
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(Strictly speaking, the `delete[] bar' should use the proper XPCOM
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de-allocator; we'll ignore that for now.)
This makes your life harder, because you need to convolute your code
to ensure that you don't leak `bar'.
Enter nsXPIDLString, which manages the ownership of the allocated
string, and automatically destroys it when the nsXPIDLString goes
out of scope:
nsIFoo* aFoo;
nsXPIDLString bar;
aFoo->GetFoo( getter_Copies(bar) );
// Use bar here...
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printf("bar is %s!\n", (const char*) bar);
// no need to remember to delete[].
Like nsCOMPtr, nsXPIDLString uses some syntactic sugar to make it
painfully clear exactly what the code expects. You need to wrap an
nsXPIDLString object with either `getter_Copies()' or
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`getter_Shares()' before passing it to a getter: these tell the
nsXPIDLString how ownership is being handled.
In the case of `getter_Copies()', the callee is allocating a copy
(which is usually the case). In the case of `getter_Shares()', the
callee is returning a const reference to `the real deal' (this can
be done using the [shared] attribute in XPIDL).
*/
#ifndef nsXPIDLString_h__
#define nsXPIDLString_h__
#include "nsCom.h"
#include "prtypes.h"
#ifndef __PRUNICHAR__
#define __PRUNICHAR__
typedef PRUint16 PRUnichar;
#endif /* __PRUNICHAR__ */
////////////////////////////////////////////////////////////////////////
// nsXPIDLString
//
// A wrapper for Unicode strings. With the |getter_Copies()| and
// |getter_Shares()| helper functions, this can be used instead of
// the "naked" |PRUnichar*| interface for |wstring| parameters in
// XPIDL interfaces.
//
class NS_COM nsXPIDLString {
private:
PRUnichar* mBuf;
PRBool mBufOwner;
PRUnichar** StartAssignmentByValue();
const PRUnichar** StartAssignmentByReference();
public:
/**
* Construct a new, uninitialized wrapper for a Unicode string.
*/
nsXPIDLString();
virtual ~nsXPIDLString();
/**
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* Return a reference to the immutable Unicode string.
*/
operator const PRUnichar*();
/**
* Make a copy of the Unicode string. Use this function in the
* callee to ensure that the correct memory allocator is used.
*/
static PRUnichar* Copy(const PRUnichar* aString);
// A helper class for assignment-by-value. This class is an
// implementation detail and should not be considered part of the
// public interface.
class NS_COM GetterCopies {
private:
nsXPIDLString& mXPIDLString;
public:
GetterCopies(nsXPIDLString& aXPIDLString)
: mXPIDLString(aXPIDLString) {}
operator PRUnichar**() {
return mXPIDLString.StartAssignmentByValue();
}
friend GetterCopies getter_Copies(nsXPIDLString& aXPIDLString);
};
friend class GetterCopies;
// A helper class for assignment-by-reference. This class is an
// implementation detail and should not be considered part of the
// public interface.
class NS_COM GetterShares {
private:
nsXPIDLString& mXPIDLString;
public:
GetterShares(nsXPIDLString& aXPIDLString)
: mXPIDLString(aXPIDLString) {}
operator const PRUnichar**() {
return mXPIDLString.StartAssignmentByReference();
}
friend GetterShares getter_Shares(nsXPIDLString& aXPIDLString);
};
friend class GetterShares;
private:
// not to be implemented
nsXPIDLString(nsXPIDLString& aXPIDLString) {}
nsXPIDLString& operator =(nsXPIDLString& aXPIDLString) { return *this; }
};
/**
* Use this function to "wrap" the nsXPIDLString object that is to
* receive an |out| value.
*/
inline nsXPIDLString::GetterCopies
getter_Copies(nsXPIDLString& aXPIDLString)
{
return nsXPIDLString::GetterCopies(aXPIDLString);
}
/**
* Use this function to "wrap" the nsXPIDLString object that is to
* receive a |[shared] out| value.
*/
inline nsXPIDLString::GetterShares
getter_Shares(nsXPIDLString& aXPIDLString)
{
return nsXPIDLString::GetterShares(aXPIDLString);
}
////////////////////////////////////////////////////////////////////////
// nsXPIDLCString
//
// A wrapper for Unicode strings. With the |getter_Copies()| and
// |getter_Shares()| helper functions, this can be used instead of
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// the "naked" |char*| interface for |string| parameters in XPIDL
// interfaces.
//
class NS_COM nsXPIDLCString {
private:
char* mBuf;
PRBool mBufOwner;
char** StartAssignmentByValue();
const char** StartAssignmentByReference();
public:
/**
* Construct a new, uninitialized wrapper for a single-byte string.
*/
nsXPIDLCString();
virtual ~nsXPIDLCString();
/**
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* Return a reference to the immutable single-byte string.
*/
operator const char*();
/**
* Make a copy of the single-byte string. Use this function in the
* callee to ensure that the correct memory allocator is used.
*/
static char* Copy(const char* aString);
// A helper class for assignment-by-value. This class is an
// implementation detail and should not be considered part of the
// public interface.
class NS_COM GetterCopies {
private:
nsXPIDLCString& mXPIDLString;
public:
GetterCopies(nsXPIDLCString& aXPIDLString)
: mXPIDLString(aXPIDLString) {}
operator char**() {
return mXPIDLString.StartAssignmentByValue();
}
friend GetterCopies getter_Copies(nsXPIDLCString& aXPIDLString);
};
friend class GetterCopies;
// A helper class for assignment-by-reference. This class is an
// implementation detail and should not be considered part of the
// public interface.
class NS_COM GetterShares {
private:
nsXPIDLCString& mXPIDLString;
public:
GetterShares(nsXPIDLCString& aXPIDLString)
: mXPIDLString(aXPIDLString) {}
operator const char**() {
return mXPIDLString.StartAssignmentByReference();
}
friend GetterShares getter_Shares(nsXPIDLCString& aXPIDLString);
};
friend class GetterShares;
private:
// not to be implemented
nsXPIDLCString(nsXPIDLCString& aXPIDLString) {}
nsXPIDLCString& operator =(nsXPIDLCString& aXPIDLString) { return *this; }
};
/**
* Use this function to "wrap" the nsXPIDLCString object that is to
* receive an |out| value.
*/
inline nsXPIDLCString::GetterCopies
getter_Copies(nsXPIDLCString& aXPIDLString)
{
return nsXPIDLCString::GetterCopies(aXPIDLString);
}
/**
* Use this function to "wrap" the nsXPIDLCString object that is to
* receive a |[shared] out| value.
*/
inline nsXPIDLCString::GetterShares
getter_Shares(nsXPIDLCString& aXPIDLString)
{
return nsXPIDLCString::GetterShares(aXPIDLString);
}
#endif // nsXPIDLString_h__