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7dd25141cd
Put simply, Error<> is a way of forcing error handling onto an API user.
Given a function like:
bool might_work();
The following code might have been written previously:
might_work(); // but what if it didn't?
The easy way to work around this is of course to [[nodiscard]] might_work.
But this doesn't work for more complex cases like, for instance, a
hypothetical read() function which might return one of _many_ errors
(typically signalled with an int, let's say).
int might_read();
In such a case, the result is often _read_, but not properly handled. Like:
return buffer.substr(0, might_read()); // but what if might_read returned an error?
This is where Error<> comes in:
typedef Error<int, 0> ReadError;
ReadError might_read();
auto res = might_read();
if (might_read.failed()) {
switch (res.value()) {
case EBADF:
...
}
}
Error<> uses clang's consumable attributes to force failed() to be
checked on an Error instance. If it's not checked, then you get smacked.
54 lines
883 B
C++
54 lines
883 B
C++
#pragma once
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#include <AK/Platform.h>
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namespace AK {
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template <typename T, auto NoErrorValue>
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class CONSUMABLE(unknown) Error {
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public:
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RETURN_TYPESTATE(unknown)
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Error()
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: t(NoErrorValue)
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{}
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RETURN_TYPESTATE(unknown)
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Error(T t)
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: t(t)
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{}
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RETURN_TYPESTATE(unknown)
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Error(Error&& other)
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: t(move(other.t))
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{
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}
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RETURN_TYPESTATE(unknown)
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Error(const Error& other)
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: t(other.t)
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{
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}
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CALLABLE_WHEN("unknown", "consumed")
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~Error() {}
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SET_TYPESTATE(consumed)
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bool failed() const {
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return t != NoErrorValue;
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}
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[[deprecated]]
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SET_TYPESTATE(consumed)
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void ignore() {}
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const T& value() const { return t; }
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bool operator==(const Error& o) { return t == o.t; }
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bool operator!=(const Error& o) { return t != o.t; }
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T t;
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};
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}
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using AK::Error;
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