An API to build slices into read parts of Reader buffer.

This commit is contained in:
Ferdinand Majerech 2014-07-24 02:42:34 +02:00
parent e493e7299d
commit 892aed303f

View file

@ -242,8 +242,158 @@ final class Reader
final Encoding encoding() @safe pure nothrow const @nogc { return encoding_; }
}
private:
/// Used to build slices of already read data in Reader buffer, avoiding allocations.
///
/// Usually these slices point to unchanged Reader data, but sometimes the data is
/// changed due to how YAML interprets certain characters/strings.
///
/// See begin() documentation.
struct SliceBuilder
{
private:
// No copying by the user.
@disable this(this);
@disable void opAssign(ref SliceBuilder);
// Reader this builder works in.
Reader reader_;
// Start of the slice om reader_.buffer_ (size_t.max while no slice being build)
size_t start_ = size_t.max;
// End of the slice om reader_.buffer_ (size_t.max while no slice being build)
size_t end_ = size_t.max;
// Stack of slice ends to revert to (see Transaction)
//
// Very few levels as we don't want arbitrarily nested transactions.
size_t[4] endStack_;
// The number of elements currently in endStack_.
size_t endStackUsed_ = 0;
@safe pure nothrow const @nogc invariant()
{
if(!inProgress) { return; }
assert(end_ <= reader_.bufferOffset_, "Slice ends after buffer position");
assert(start_ <= end_, "Slice start after slice end");
}
// Is a slice currently being built?
bool inProgress() @safe pure nothrow const @nogc
{
assert(start_ == size_t.max ? end_ == size_t.max :
end_ != size_t.max, "start_/end_ are not consistent");
return start_ != size_t.max;
}
public:
/// Begin building a slice.
///
/// Only one slice can be built at any given time; before beginning a new slice,
/// finish the previous one (if any).
///
/// The slice starts at the current position in the Reader buffer. It can only be
/// extended up to the current position in the buffer; Reader methods get() and
/// forward() move the position. E.g. it is valid to extend a slice by write()-ing
/// a string just returned by get() - but not one returned by prefix() unless the
/// position has changed since the prefix() call.
void begin() @system pure nothrow @nogc
{
assert(!inProgress, "Beginning a slice while another slice is being built");
assert(endStackUsed_ == 0, "Slice stack not empty at slice begin");
start_ = reader_.bufferOffset_;
end_ = reader_.bufferOffset_;
}
/// Finish building a slice and return it.
///
/// Any Transactions on the slice must be committed or destroyed before the slice
/// is finished.
dstring finish() @system pure nothrow @nogc
{
assert(inProgress, "sliceFinish called without sliceBegin");
assert(endStackUsed_ == 0, "Finishing a slice with running transactions.");
const result = cast(dstring)reader_.buffer_[start_ .. end_];
start_ = end_ = size_t.max;
return result;
}
/// Write a string to the slice being built.
///
/// Data can only be written up to the current position in the Reader buffer.
///
/// If str is a string returned by a Reader method, and str starts right after the
/// end of the slice being built, the slice is extended (trivial operation).
///
/// See_Also: begin
void write(dstring str) @system pure nothrow @nogc
{
assert(inProgress, "sliceWrite called without sliceBegin");
// If str starts at the end of the slice (is a string returned by a Reader
// method), just extend the slice to contain str.
if(str.ptr == reader_.buffer_.ptr + end_)
{
end_ += str.length;
}
// Even if str does not start at the end of the slice, it still may be returned
// by a Reader method and point to buffer. So we need to memmove.
else
{
core.stdc.string.memmove(reader_.buffer_.ptr + end_, cast(dchar*)str.ptr,
str.length * dchar.sizeof);
end_ += str.length;
}
}
/// Write a character to the slice being built.
///
/// Data can only be written up to the current position in the Reader buffer.
///
/// See_Also: begin
void write(dchar c) @system pure nothrow @nogc
{
assert(inProgress, "sliceWrite called without sliceBegin");
reader_.buffer_[end_++] = c;
}
private:
// Push the current end of the slice so we can revert to it if needed.
//
// Used by Transaction.
void push() @system pure nothrow @nogc
{
assert(inProgress, "slicePush called without sliceBegin");
assert(endStackUsed_ < endStack_.length, "Slice stack overflow");
endStack_[endStackUsed_++] = end_;
}
// Pop the current end of endStack_ and set the end of the slice to the popped
// value, reverting changes since the old end was pushed.
//
// Used by Transaction.
void pop() @system pure nothrow @nogc
{
assert(inProgress, "slicePop called without sliceBegin");
assert(endStackUsed_ > 0, "Trying to pop an empty slice stack");
end_ = endStack_[--endStackUsed_];
}
// Pop the current end of endStack_, but keep the current end of the slice, applying
// changes made since pushing the old end.
//
// Used by Transaction.
void apply() @system pure nothrow @nogc
{
assert(inProgress, "sliceApply called without sliceBegin");
assert(endStackUsed_ > 0, "Trying to apply an empty slice stack");
--endStackUsed_;
}
}
// Decode an UTF-8/16/32 buffer to UTF-32 (for UTF-32 this does nothing).
//
// Params: