Re: The 'BASE Attribute

[Dave Papay M/S 7G32 x2791 <papayd@GTEWD.MTV.GTEGSC.COM>]

Program Validation L <pvl@CIX.COMPULINK.CO.UK> writes:

>We are confused by the meaning of the 'BASE attribute. For example, the
>LRM states that a fixed point type declaration of the form:
>
>type T is delta D range L .. R;
>
>is, by definition, equivalent to the following declarations:
>
>type fixed_point_type is new predefined_fixed_point_type;
>subtype T is fixed_point_type
>  range fixed_point_type(L) .. fixed_point_type(R);
>
>We would therefore expect T to denote the (implicitly declared) subtype,
>and T'BASE to denote the anonymous type fixed_point_type. This would mean
>that T'DELTA is valid, whilst T'BASE'DELTA is invalid, since P'DELTA is
>only defined for fixed point subtypes.

T'BASE'DELTA is legal, since in 3.3(4) the LRM states: "A type is a subtype
of itself..."

Also, although the description for the 'DELTA attribute in 3.5.10(4) states
that it "Yields the value of the delta specified in the fixed accuracy
definition for the *subtype* T" (emphasis added), 3.5.10(2) states that the
attributes listed below (which includes 'DELTA) are define "for every fixed
point *type or subtype* T" (again, emphasis added).  This paragraph also
explains why T is referred to as a subtype in some contexts, and as a type in
others.

Hope this helps.

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