gecko-dev/dom/bindings/DOMString.h

150 lines
4.6 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef mozilla_dom_DOMString_h
#define mozilla_dom_DOMString_h
#include "nsStringGlue.h"
#include "nsStringBuffer.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/Maybe.h"
#include "nsDOMString.h"
namespace mozilla {
namespace dom {
/**
* A class for representing string return values. This can be either passed to
* callees that have an nsString or nsAString out param or passed to a callee
* that actually knows about this class and can work with it. Such a callee may
* call SetStringBuffer on this object, but only if it plans to keep holding a
* strong ref to the stringbuffer!
*
* The proper way to store a value in this class is to either to do nothing
* (which leaves this as an empty string), to call SetStringBuffer with a
* non-null stringbuffer, to call SetNull(), or to call AsAString() and set the
* value in the resulting nsString. These options are mutually exclusive!
* Don't do more than one of them.
*
* The proper way to extract a value is to check IsNull(). If not null, then
* check HasStringBuffer(). If that's true, check for a zero length, and if the
* length is nonzero call StringBuffer(). If the length is zero this is the
* empty string. If HasStringBuffer() returns false, call AsAString() and get
* the value from that.
*/
class MOZ_STACK_CLASS DOMString {
public:
DOMString()
: mStringBuffer(nullptr)
, mLength(0)
, mIsNull(false)
{}
~DOMString()
{
MOZ_ASSERT(mString.empty() || !mStringBuffer,
"Shouldn't have both present!");
}
operator nsString&()
{
return AsAString();
}
nsString& AsAString()
{
MOZ_ASSERT(!mStringBuffer, "We already have a stringbuffer?");
MOZ_ASSERT(!mIsNull, "We're already set as null");
if (mString.empty()) {
mString.construct();
}
return mString.ref();
}
bool HasStringBuffer() const
{
MOZ_ASSERT(mString.empty() || !mStringBuffer,
"Shouldn't have both present!");
MOZ_ASSERT(!mIsNull, "Caller should have checked IsNull() first");
return mString.empty();
}
// Get the stringbuffer. This can only be called if HasStringBuffer()
// returned true and StringBufferLength() is nonzero. If that's true, it will
// never return null.
nsStringBuffer* StringBuffer() const
{
MOZ_ASSERT(!mIsNull, "Caller should have checked IsNull() first");
MOZ_ASSERT(HasStringBuffer(),
"Don't ask for the stringbuffer if we don't have it");
MOZ_ASSERT(StringBufferLength() != 0, "Why are you asking for this?");
MOZ_ASSERT(mStringBuffer,
"If our length is nonzero, we better have a stringbuffer.");
return mStringBuffer;
}
// Get the length of the stringbuffer. Can only be called if
// HasStringBuffer().
uint32_t StringBufferLength() const
{
MOZ_ASSERT(HasStringBuffer(), "Don't call this if there is no stringbuffer");
return mLength;
}
void SetStringBuffer(nsStringBuffer* aStringBuffer, uint32_t aLength)
{
MOZ_ASSERT(mString.empty(), "We already have a string?");
MOZ_ASSERT(!mIsNull, "We're already set as null");
MOZ_ASSERT(!mStringBuffer, "Setting stringbuffer twice?");
MOZ_ASSERT(aStringBuffer, "Why are we getting null?");
mStringBuffer = aStringBuffer;
mLength = aLength;
}
void SetNull()
{
MOZ_ASSERT(!mStringBuffer, "Should have no stringbuffer if null");
MOZ_ASSERT(mString.empty(), "Should have no string if null");
mIsNull = true;
}
bool IsNull() const
{
MOZ_ASSERT(!mStringBuffer || mString.empty(),
"How could we have a stringbuffer and a nonempty string?");
return mIsNull || (!mString.empty() && mString.ref().IsVoid());
}
void ToString(nsAString& aString)
{
if (IsNull()) {
SetDOMStringToNull(aString);
} else if (HasStringBuffer()) {
if (StringBufferLength() == 0) {
aString.Truncate();
} else {
StringBuffer()->ToString(StringBufferLength(), aString);
}
} else {
aString = AsAString();
}
}
private:
// We need to be able to act like a string as needed
Maybe<nsAutoString> mString;
// For callees that know we exist, we can be a stringbuffer/length/null-flag
// triple.
nsStringBuffer* mStringBuffer;
uint32_t mLength;
bool mIsNull;
};
} // namespace dom
} // namespace mozilla
#endif // mozilla_dom_DOMString_h