What is Expressiveness in a Computer Language

[Rob Thorpe]

Dr.Ruud wrote:
> Rob Thorpe schreef:
> > Dr.Ruud:
> >> Marshall:
>
> >>> "dynamic types." I don't have a firm definition for
> >>> that term, but my working model is runtime type tags. In which
> >>> case, I would say that among statically typed languages,
> >>> Java does have dynamic types, but C does not. C++ is
> >>> somewhere in the middle.
> >>
> >> C has union.
> >
> > That's not the same thing.
>
> That is your opinion. In the context of this discussion I don't see any
> problem to put C's union under "dynamic types".

Lets put it like this:-
1. In C++ and Java it is possible to make a variable that can A)Take on
many different types and B)Where the programmer can test what the type
is.
2. In C it is possible to make a variable that can do 1A but not 1B.

This is a statement of fact, not opinion.

I call languages that do #1 dynamically typed, in line with common
usage.

> > The value of a union in C can be any of a
> > set of specified types.  But the program cannot find out which, and
> > the language doesn't know either.
> >
> > With C++ and Java dynamic types the program can test to find the type.
>
> When such a test is needed for the program with the union, it has it.

What do you mean?
There is no way to test the type of the value inside a union in C.