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basics.adoc: include cpp fragments

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This commit is contained in:
Jean-Louis Leroy
2025-10-21 12:50:46 -04:00
parent c7bc263e81
commit 9ecf9158f9
2 changed files with 21 additions and 17 deletions
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6
doc/modules/ROOT/examples/ast.cpp
View File

@@ -43,11 +43,14 @@ using boost::openmethod::virtual_ptr;
BOOST_OPENMETHOD(postfix, (virtual_ptr<const Node> node, std::ostream& os), void);
// tag::variable_overrider[]
BOOST_OPENMETHOD_OVERRIDE(
postfix, (virtual_ptr<const Variable> var, std::ostream& os), void) {
os << var->v;
}
// end::variable_overrider[]
// tag::plus_overrider[]
BOOST_OPENMETHOD_OVERRIDE(
postfix, (virtual_ptr<const Plus> plus, std::ostream& os), void) {
postfix(plus->left, os);
@@ -55,6 +58,7 @@ BOOST_OPENMETHOD_OVERRIDE(
postfix(plus->right, os);
os << " +";
}
// end::plus_overrider[]
BOOST_OPENMETHOD_OVERRIDE(
postfix, (virtual_ptr<const Times> times, std::ostream& os), void) {
@@ -64,7 +68,9 @@ BOOST_OPENMETHOD_OVERRIDE(
os << " *";
}
// tag::class_registration[]
BOOST_OPENMETHOD_CLASSES(Node, Variable, Plus, Times);
// end::class_registration[]
int main() {
boost::openmethod::initialize();

32
doc/modules/ROOT/pages/basics.adoc
View File

@@ -37,11 +37,10 @@ inline auto postfix(virtual_ptr<const Node> node, std::ostream& os) -> void {
Before we can call the method, we need to define overriders. For that we use the
xref:BOOST_OPENMETHOD_OVERRIDE.adoc[BOOST_OPENMETHOD_OVERRIDE] macro:
```c++
BOOST_OPENMETHOD_OVERRIDE(postfix, (virtual_ptr<const Variable> var, std::ostream& os), void) {
os << var->v;
}
```
[source,cpp]
----
include::{examplesdir}/ast.cpp[tag=variable_overrider]
----
The overrider must have virtual parameters in the same positions as in the
method. The classes in the method's virtual parameters must be accessible,
@@ -53,13 +52,10 @@ The non-virtual parameters must have exactly the same types as in the method.
Let's look at another overrider:
```c++
BOOST_OPENMETHOD_OVERRIDE(postfix, (virtual_ptr<const Plus> plus, std::ostream& os), void) {
postfix(plus->left, os);
os << ' ';
postfix(plus->right, os);
}
```
[source,cpp]
----
include::{examplesdir}/ast.cpp[tag=plus_overrider]
----
This one calls `postfix` recursively to print the left and right
sub-expressions. Note that we call the method just like an ordinary function.
@@ -67,18 +63,20 @@ sub-expressions. Note that we call the method just like an ordinary function.
`postfix` expects a `virtual_ptr<const Node>`, and we are passing it a _plain_
_reference_ to a `Plus` object. This works because `virtual_ptr` has conversion
constructors from plain references or pointers to an object, or from other
`virtual_ptr` to compatible classes.
`virtual_ptr`{empty}s to compatible classes.
There are two more things we need to do.
OpenMethod is a library, not a compiler. It needs to be made aware of all the
classes that may be used as virtual parameters, and in method calls, and their
inheritance relationships. We do this using the
inheritance relationships. We do this with the
xref:BOOST_OPENMETHOD_CLASSES.adoc[BOOST_OPENMETHOD_CLASSES] macro:
```c++
BOOST_OPENMETHOD_CLASSES(Node, Variable, Plus, Times);
```
[source,cpp]
----
include::{examplesdir}/ast.cpp[tag=class_registration]
----
Classes can be registered multiple times, in any order, and incrementally. Every
direct base of a class must appear together with it in at least one call to