Add ParseResult infrastructure

ParseInput is passed into all parsing methods and simply acts as
a shared container which can hold a generic success or error value.
When it is transformed into a result value, it must be returned to
its parent immediately, who can decide what to do with it.

ParseResult is the type returned when a ParseInput is set to success
or error. It casts itself to a strong type representing the returned
value, and is used by specifying ParseResult<ResultType> instead of
just ResultType for the method return type.

ParseTypeImpl is just the implementation of the two above which handles
moving between them. It also adds some debug functionality in case
the error catching code is incorrect or insufficient and it would be
preferably to always have a stack trace.

It is important to use this infrastructure in a thread-local manner,
such that you don't re-use an input already in use and always bubble
up on any success or error.

A constrained example:

class Parser {

    val shared = ParseTypeImpl<>()

    fun parse(file: File): Pair<Output, Output> {
        // Reset the shared object
        val input = shared.reset()

        // Pass it to be used by the parsing method
        var result = parseOutput(input, file.read())

        // Verify the result
        if (result.isError()) {
            // Bubble up error if necessary
            throw Exception(result.errorMessage, result.exception)
        }

        // Save the result (as it will be lost when the input is reused)
        val one = result.result

        // Parse something else
        result = parseOutput(input, file.read())

        // Same verification
        if (result.isError()) {
            // Bubble up error if necessary
            throw Exception(result.errorMessage, result.exception)
        }

        val two = result.result
        return one to two
    }

    fun parseOutput(input: Input, read: Object): ParseResult<Output> {
        return if (read == null) {
            input.error("Something went wrong")
        } else {
            input.success(read)
        }
    }
}

Bug: 135203078

Change-Id: I532d0047e67f80fd925b481dac8823ab45ad0194

0 files changed, 0 insertions, 0 deletions