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Message: [QUOTE="Rob Dekker, post: 3542160"] Hi Jim, The restriction you talk about is probably the LRM 7.3.5 rule : "The type of the operand of a type conversion must be determinable independent of the context (in particular, independent of the target type)." Why is this in there ? I'm not entirely sure, but it does make sense from a wider point of view. Here is the type conversion in simplified syntax : target_type( expression ) 'expression' is 'cast' to type 'target_type'. That means that 'target_type' is not the same as the expression type. So how do we know which type 'expression' can or should be ? We don't ! That's why they put the rule in there that the type of the expression should be determinible without context info. Later in 7.3.5, it is stated that the type conversion is only allowed if the target type is at least 'closely related' to the expression type. 'closely related' is then defined as a certain dependency between expression type and target type. Other type conversions are not allowed (except for some 'universal' implicit type conversions). So it seems that they could have made the type-inference rule dependent on the 'closely related' semantics of the construct. Maybe something like this : "The type of the operand of a type conversion must be determinable independent of the context, but taken into consideration that the type of the expression and the target type must be closely related." This sentence is not entirely correct yet, since implicit (universal) type conversions would need to be included, but it would allow for overloading to determine the expression type based on the target type in some form. This could be a headache for compiler builders, since VHDL hardly ever has special-purpose type-conditions like this, and remember this was written before 1987, when compiler technology was not yet so sophisticated as it is today. So I think that by making the type conversion rule simple, it would be easier to bring out a full VHDL parser, and that's why the rules are a bit easier on the compiler. Any way, that's my 2 cts on this issue. Rob Dekker Verific [/QUOTE]

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