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90 lines
2.5 KiB
ReStructuredText
90 lines
2.5 KiB
ReStructuredText
variables
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=========
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Working with variables is easy with Sol, and behaves pretty much like any associative array / map structure you've dealt with previously. Given this lua file that gets loaded into Sol:
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reading
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-------
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.. code-block:: lua
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:caption: variables.lua
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config = {
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fullscreen = false,
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resolution = { x = 1024, y = 768 }
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}
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.. code-block:: cpp
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:caption: main.cpp
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int main () {
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sol::state lua;
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lua.script_file( variables.lua );
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return 0;
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}
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You can interact with the variables like this:
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.. code-block:: cpp
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:caption: main.cpp extended
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#include <utility> // for std::pair
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int main () {
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sol::state lua;
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lua.script_file( variables.lua );
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// the type "state" behaves exactly like a table!
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bool isfullscreen = lua["config"]["fullscreen"]; // can get nested variables
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sol::table config = lua["config"];
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// can also get it using the "get" member function
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// auto replaces the unqualified type name
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auto resolution = config.get<sol::table>( "config" );
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// table and state can have multiple things pulled out of it too
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std::pair<int, int> xyresolution = resolution.get<int, int>( "x", "y" );
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// As an example, you can also pull out a tuple as well
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// std::tuple<int, int> xyresolution = resolution.get<int, int>( "x", "y" );
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return 0;
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}
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From this example, you can see that there's many ways to pull out the varaibles you want. Some can be more safe than others. For example, to determine if a nested variable exists or not, you can use ``auto`` to capture the value of a ``table[key]`` lookup, and then use the ``.valid()`` method:
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.. code-block:: cpp
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:caption: safe lookup
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auto bark = lua["config"]["bark"];
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if (bark.valid()) {
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// branch not taken: config / bark is not a variable
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}
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else {
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// Branch taken: config is a not a variable
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}
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This comes in handy when you want to check if a nested variable exists. You can also check if a toplevel variable is present or not by using ``sol::optional``, which also checks if the type you're trying to get is of a specific type:
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.. code-block:: cpp
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:caption: optional lookup
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sol::optional<int> not_an_integer = lua["config"]["fullscreen"];
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if (not_an_integer) {
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// Branch not taken: value is not an integer
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}
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sol::optoinal<bool> is_a_boolean = lua["config"]["fullscreen"];
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if (is_a_boolean) {
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// Branch taken: the value is a boolean
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}
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sol::optional<double> does_not_exist = lua["not_a_variable"];
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if (does_not_exist) {
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// Branch not taken: that variable is not present
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}
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