memoize.bbclass

def memoize(d, varname, func):
    """Calculate the result of func once, replacing the value in the metadata.
    
    This will run the function once rather than every time it's used, but unlike
    immediate expansion, this initial expansion occurs the first time it's used.

    Example Usage:

        TESTVAR = "${@memoize(d, 'TESTVAR', lambda: myfunction(d) or '')}"
        TESTVAR[vardepvalue] = "${TESTVAR}"
    """
    value = func()
    d.setVar(varname, value)
    return value