adh@minster.york.ac.uk (08/30/89)
In article <20600004@inmet> stt@inmet writes: >The usual fix is to >determine which package calls which other package at >elaboration time, and place a pragma Elaborate (see LRM 10.5:3) >in the calling package referencing the called package. >Note that if the called package calls other packages, there >may be a need to include additional pragma Elaborates on >those lower level packages. Pragma Elaborate only forces >elaboration for a single level of dependency. Hopefully, >Ada 9X will fix it so that it forces elaboration for >the closure of dependencies... I assume that the possible need for additional pragma ELABORATEs is because there may be further cases of package body being called before it has elaborated that will be exposed when the first error is fixed. The problem I have is with the suggestion that pragma ELABORATE should be changed to force elaboration of all package (actually library unit?) bodies in the closure of dependencies, as part of 9X. I don't think this is necessary - the pragma is intended only to indicate that prior elaboration of a particular body, whose specification will already have been elaborated, is required. Indeed, I can contrive examples where the current pragma ELABORATE will ensure elaboration completes, but the proposed new semantics would prevent elaboration (i.e. the package whose body carries the pragma ELABORATE is in the closure of the bodies of units depended upon by the package named by the pragma ELABORATE). Or am I missing somthing? Andy Hutcheon (adh@uk.ac.york.minster)
stt@inmet (09/01/89)
We have proposed that pragma Elaborate be changed/augmented as part of Ada9X. The proposal suggests that pragma Elaborate cause the "early" elaboration of all of the bodies of all packages in the "with" closure of the specified package. This is useful because a package generally doesn't "know" whether any of its subprograms will be called at elaboration time, and hence whether it should pragma-elaborate the packages it depends on. Furthermore, due to mutual dependency between packages, it is often hard to insert pragma Elaborates as needed. However, the closure approach doesn't need to specify a specific ordering among the package bodies making up the closure, and hence isn't affected by mutual dependency issues. The wording of the proposal is such that any conflict created by elaborating the closure of with dependencies is resolved in favor of direct pragma Elaborates. Given that, there is no reason why linkers couldn't implement the proposed semantics now. However, the goal of the proposal is to reduce the rehosting surprises currently possible due to distinct implementations of elaboration-order determination, by making the closure implementation approach a requirement of the language. Tucker Taft Intermetrics, Inc. Cambridge, MA 02138