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self_vs_super

This example illustrates the differences between a message to self and a super call when calling an inherited meta-predicate. See the comments in the code for details.

For an in-depth discussion of these concepts, see the corresponding Handbook glossary entries, the section on "Predicates", and the reference pages on the the execution-context built-in methods.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the example:

logtalk_load(self_vs_super(loader)).

Illustrate the differences between sending a message to self and making a super call to call an inherited meta-predicate by using a foo/1 predicate defined in user:

%%table
foo(X).

The super calls preserve sender and therefore the foo/1 predicate is called by the meta-predicate in the context of user:

%%table
proto::meta_super(foo, X).

<!-- Execution context for the parent object meta/2 meta-predicate: self: proto this: parent sender: user

X = 1 ? ; X = 2 ? ; X = 3. -->

Messages to self reset sender and therefore the foo/1 predicate is called in the context of proto, hence the existence error:

catch(proto::meta_self(foo, X), Error, true).

<!-- Execution context for the parent object meta/2 meta-predicate: self: proto this: parent sender: proto

Error = error(existence_error(procedure,foo/1),logtalk(call(foo(_307)),c(proto,proto,r(user,proto,c(user,user,r(user,proto,[],[])),[])))). -->