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doc: registry context

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This commit is contained in:
Michele Caini
2022-08-02 08:41:45 +02:00
parent 504c7b5d6d
commit acc95bd9b7
1 changed files with 17 additions and 6 deletions
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23
docs/md/entity.md
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@@ -878,17 +878,23 @@ The context is returned via the `ctx` functions and offers a minimal set of
feature including the following:
```cpp
// creates a new context variable by type
// creates a new context variable by type and returns it
registry.ctx().emplace<my_type>(42, 'c');
// creates a new context variable with a name
registry.ctx().emplace_hint<my_type>("my_variable"_hs, 42, 'c');
// creates a new named context variable by type and returns it
registry.ctx().emplace_as<my_type>("my_variable"_hs, 42, 'c');
// inserts or assigns a context variable by (deduced) type and returns it
registry.ctx().insert_or_assign(my_type{42, 'c'});
// inserts or assigns a named context variable by (deduced) type and returns it
registry.ctx().insert_or_assign("my_variable"_hs, my_type{42, 'c'});
// gets the context variable by type as a non-const reference from a non-const registry
auto &var = registry.ctx().at<my_type>();
auto &var = registry.ctx().get<my_type>();
// gets the context variable by name as a const reference from either a const or a non-const registry
const auto &cvar = registry.ctx().at<const my_type>("my_variable"_hs);
const auto &cvar = registry.ctx().get<const my_type>("my_variable"_hs);
// resets the context variable by type
registry.ctx().erase<my_type>();
@@ -930,6 +936,11 @@ Read-only aliased properties are created using const types instead:
registry.ctx().emplace<const time &>(clock);
```
Note that `insert_or_assign` doesn't support aliased properties and users must
necessarily use `emplace` or `emplace_as` for this purpose.<br/>
When `insert_or_assign` is used to update an aliased property, it _converts_
the property itself into a non-aliased one.
From the point of view of the user, there are no differences between a variable
that is managed by the registry and an aliased property. However, read-only
variables aren't accessible as non-const references:
@@ -937,7 +948,7 @@ variables aren't accessible as non-const references:
```cpp
// read-only variables only support const access
const my_type *ptr = registry.ctx().find<const my_type>();
const my_type &var = registry.ctx().at<const my_type>();
const my_type &var = registry.ctx().get<const my_type>();
```
Aliased properties can be erased as it happens with any other variable.