What is the rationale behind typedef vs struct/union/enum, couldn't there be only one namespace?

Question

In C if I declare a struct/union/enum:

struct Foo { int i ... }

when I want to use my structure I need to specify the tag:

struct Foo foo;

To loose this requirement, I have to alias my structure using typedef:

typedef struct Foo Foo;

Why not have all types/structs/whatever in the same "namespace" by default? What is the rationale behind the decision of requiring the declaration tag at each variable declaration (unless typdefe'd) ???

Many other languages do not make this distinction, and it seems that it's only bringing an extra level of complexity IMHO.

Answer 1

Structures/records were a very early pre-C addition to B, just after Dennis Ritchie added a the basic 'typed' structure. I believe that the original struct syntax did not have a tag at all, for every variable you made an anonymous struct:

struct {
    int  i;
    char a[5];
} s;

Later, the tag was added to enable reuse of structure layout, but it wasn't really regarded as real 'type'. Also, removing the struct/union would make parsing impossible:

/* is Foo a union or a struct? */
Foo { int i; double x; };
Foo s;

or break the 'declaration syntax mimics expression syntax' paradigm that is so fundamental to C.

I suspect that typedef was added much later, possible a few years after the 'birth' of C.

The argument "C was the highest level language at the time." does not seem true. Algol-68 predates it and has records as proper types. The same holds for Pascal.

If you like to know more about the history of C you might find Ritchie's "The Development of the C Language" an interesting read.