RE: newbie can't get exceptions to work!

[Wilhelm.Spickermann@t-online.de (Wilhelm Spickermann)]

On 05-Apr-01 Jeff Shipman wrote:
...
> generic
>    LEN : NATURAL := 100;      -- Size of the stack (default 100
>    type ELM is private;       -- Used to store element type
> 
>    package GEN_STACK is
>       STACK_ERROR : exception;        -- Raised when something bad
> happens.
>       
>       procedure PUSH(E : in ELM);     -- Push E into the stack
>       procedure POP(E : out ELM);     -- Pop element from stack;
> store
> in E
>       
>       function  FULL return BOOLEAN;  -- Returns TRUE if stack is
...
>    exception
>       when STACK_ERROR =>
...
> When I try to compile, I get the following errors:
> 
> use_gen_stack.adb:214:12: "STACK_ERROR" is not visible
> use_gen_stack.adb:214:12: multiple use clauses cause hiding

What should the program do, if You write "PUSH(4)"? Should it push into
INT_STACK or INT2_STACK?

You have created six _different_ exceptions, which are all called
STACK_ERROR. The compiler cannot possibly know which one You try to
handle. You could use names like FLOAT_STACK.STACK_ERROR etc.

You will run into the same problems with the other entities of the
generic package.

Such a "generic abstract data object" is very practical if only one
instantiation is needed at every place of use. If You really need
several stack in interleaved usage, you need a "generic abstract data
type".

Wilhelm