67 lines
2.3 KiB
Markdown
67 lines
2.3 KiB
Markdown
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# Try-catch statements
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**NOTE**: Try-catches are not yet supported. They are a planned feature, but will take a long time until they are implemented
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A try-catch statement will try running the code in the `try` block, and if any exceptions are thrown, they are going to be handled by the `catch` statement (if the types of the exceptions match, of course).
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## Catches
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A catch is a part of the try-catch statement, that consists of a single "parameter" of sorts, that is the type of exception that this catch is going to handle. This can be a contract as well, but due to some inefficiencies in that regard, it's recommended to handle separate classes.
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### Nameless catches
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If a catch doesn't specify the name of the exception it's getting, then the catch will only listen for the exception thrown. Such catches can specify multiple types they're listening for.
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### Typeless catch
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Such catch doesn't have any parenthesis and it listens for all exceptions.
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### Syntax
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```c++
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catch (Type name) statement;
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// Or
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catch (Type1, Type2, Type3, Type3, ... TypeN) statement;
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// Or
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catch statement;
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```
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### Order of catch executions
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Since a try-catch can have multiple catches, they will be executed in order. If one of them breaks out of the try-catch statement, via `break`, `goto`, another `throw` or `return`, the chain of catches is going to be broken and the try-catch statement is going to be left.
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## Throw
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The throw statement accepts an expression of any type, or no expression. The throw statement acts like the return statement, but instead of a meaningful return value, it communicates to the caller that something has went wrong, and sends the provided value to the caller. The thrown value propagates the call stack, until a caller that has provided an appropriate catch is reached.
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## Possible optimizations
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Two catches that have the same types will be combined, for example:
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```c++
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void main() {
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try func();
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catch (int err) ...;
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catch (int) ...;
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}
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```
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Will result in code which looks like this:
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```c++
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void main() {
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try func();
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catch (int err) {
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catch1 ...;
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catch2 ...;
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}
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}
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```
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If a catch catches a type that the function doesn't throw, the catch will be omitted.
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## ++C architecture for catching exceptions
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In the ++C ecosystem, throw-catch works by passing catch callbacks to the function calls inside the `try` statement.
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