Currently using Rebuild is only useful when parsing, because the dictionary gets filled with value copys:

    d = Struct(
        "foo" / Int32ul,
        "bar" / Rebuild(Int32ul, lambda ctx: ctx.baz),
        "baz" / Rebuild(Int32ul, lambda ctx: ctx.foo),
    )
    data = b'\x04\x00\x00\x00\x04\x00\x00\x00\x04\x00\x00\x00'
    obj = d.parse(data)
    # Container(foo=4, bar=4, baz=4)

However this isn't useful when building, because you don't know in later stages about the rebuilding, and when the parameters change, you'd need to change all of them.

With this change it is possible to put lambda ctx: ctx.foo into the Container, which get resolved immediately, when accessed. (See the test case)

This could be expanded upon, so that Rebuild itself just add these to the Container when parsing, or that a possible preprocessing step adds these before building.

The inspect hack is necessary to not break the existing behaviour of Lazy adding lambdas into the Container, which get resolved and return not the lambda, but the resulting value directly.