What is pragma preelaborated used for?

What is pragma preelaborated used for?

[wzm]

Though I have read ARM - 10.2.1 Elaboration Control,I don't understand
pragma preelabrated and pragma pure well,can some bosy give me a
detailed lesson?

Re: What is pragma preelaborated used for?

[Robert Dewar]

wzm@venusic.com (wzm) wrote in message news:<90bbca14.0107271856.324b779f@posting.google.com>...
> Though I have read ARM - 10.2.1 Elaboration Control,I don't understand
> pragma preelabrated and pragma pure well,can some bosy give me a
> detailed lesson?

What you need is a good Ada text book, trying to learn stuff like
this from the ARM is very difficult for most people. Everything is
there in the ARM in terms of what the semantics are, but for 
understanding motivation and what things are used for, you are
expected to understand that in advance. For example, when you read
about an IF statement, you are expected to be familiar with the
general idea of conditional execution.

For a less familiar area like elaboration, it's really hard to expect
to be able to understand motivations from the ARM, and documents
like tutorials, text books, and the rationale are far better resources.

The trouble with asking general questions in a newsgroup is

a) no one can spend the time and care that went into writing a text
book chapter on the subject.

b) you are likely to get answers from people who don't really know what
they are talking about, the blind leading the blind down the wrong
alley is an all-to-frequent occurrence in newsgroups :-)

I would especially expect b) to be true for the question you asked,
since Preelaborate/Pure are tricky features that serve at least three
quite different functions in the language.