Proposal: Pointer::Appender#to_slice

[straight-shoota]

When using a Pointer::Appender, somteimes you do not know how much data you're going to append beforehand (only an upper limit). But to continue, you need a slice of the appended data.

I'm proposing to add a method Pointer::Appender#to_slice for that. It returns a slice from the appender start and of the size of appended data. The implementation is trivial:

struct Pointer::Appender
    def to_slice : Slice(T)
      @start.to_slice(size)
    end
end

There are some use cases in stdlib, where such a method could replace the manual slice creation:

crystal/src/crystal/system/print_error.cr

Lines 21 to 37 in c048851

	appender = utf8.to_unsafe.appender
	String.each_utf16_char(bytes) do |char|
	if appender.size > utf8.size - char.bytesize
	# buffer is full (char won't fit)
	print_error utf8.to_slice[0...appender.size]
	appender = utf8.to_unsafe.appender
	end
	char.each_byte do |byte|
	appender << byte
	end
	end
	if appender.size > 0
	print_error utf8.to_slice[0...appender.size]
	end

crystal/src/crystal/system/win32/file_descriptor.cr

Lines 420 to 426 in c048851

	appender = @@utf8_buffer.to_unsafe.appender
	String.each_utf16_char(utf16_buffer.to_slice[..index]) do |char|
	char.each_byte do |byte|
	appender << byte
	end
	end
	@@buffer = @@utf8_buffer[0, appender.size]