# Class FunctionInvoker<TReturn>

OptimaJet.Workflow.Core.CodeActions.FunctionInvoker<TReturn>

Stores asynchronous workflow functions by transition name and invokes them for process instances.

Namespace: [OptimaJet.Workflow.Core.CodeActions](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/)

```csharp
public abstract class FunctionInvoker<TReturn>
```

## Type Hierarchy

-   FunctionInvoker<TReturn> Current type
    -   [ExpressionsInvoker](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/ExpressionsInvoker/)
    -   [SubprocessNameGetterInvoker](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/SubprocessNameGetterInvoker/)

## Constructors

`public FunctionInvoker()` 

Initializes a new instance of the [FunctionInvoker<TReturn>](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn/) type.

## Properties

`protected abstract FunctionInvoker<TReturn>.InvokerNotFoundReactionType InvokerNotFoundReaction { get; }` 

Gets the behavior applied by the [FunctionInvoker<TReturn>.InvokeAsync(TransitionDefinition, ProcessInstance)](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn/) methods when no function is registered for the requested transition.

`public abstract string FunctionName { get; }` 

Gets the label included in compilation-error and missing-function messages.

## Methods

`public void RegisterFunctions(IDictionary<string, Func<ProcessInstance, Task<TReturn>>> functions)` 

Registers compiled transition functions by transition name.

### Parameters

| Name | Type | Description |
| --- | --- | --- |
| `functions` | `IDictionary<String, ProcessInstance, Task<TReturn>>` | A map from transition names to functions that evaluate a [ProcessInstance](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.Model/ProcessInstance/). |

### Exceptions

| Type | Description |
| --- | --- |
| `ArgumentException` | Thrown when a function is already registered for one of the supplied transition names. |
| `ArgumentNullException` | Thrown when one of the supplied transition names is [null](https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/null). |

`public Task<TReturn> InvokeAsync(TransitionDefinition transitionDefinition, ProcessInstance processInstance)` 

Invokes the compiled function identified by `transitionDefinition` for the supplied `processInstance`.

### Parameters

| Name | Type | Description |
| --- | --- | --- |
| `transitionDefinition` | `TransitionDefinition` | The [TransitionDefinition](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.Model/TransitionDefinition/) whose TransitionDefinition.Name is used for lookup. |
| `processInstance` | `ProcessInstance` | The [ProcessInstance](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.Model/ProcessInstance/) passed to the selected function. |

### Returns

| Type | Description |
| --- | --- |
| `Task<TReturn>` | The value returned by the selected function, or [default](https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/default) for `TReturn` when no function is registered and the derived invoker uses [FunctionInvoker<TReturn>.InvokerNotFoundReactionType.ReturnDefault](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn.InvokerNotFoundReactionType/). |

### Exceptions

| Type | Description |
| --- | --- |
| `Exception` | Thrown when no function is registered for the transition and the derived invoker does not return a default value for missing functions. Exceptions raised by a registered function are propagated. |
| `ArgumentNullException` | Thrown when TransitionDefinition.Name is [null](https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/null). |

`public Task<TReturn> InvokeAsync(string transitionName, ProcessInstance processInstance)` 

Invokes the compiled function identified by `transitionName` for the supplied `processInstance`.

### Parameters

| Name | Type | Description |
| --- | --- | --- |
| `transitionName` | `String` | The transition name used to locate the compiled function. |
| `processInstance` | `ProcessInstance` | The [ProcessInstance](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.Model/ProcessInstance/) passed to the selected function. |

### Returns

| Type | Description |
| --- | --- |
| `Task<TReturn>` | The value returned by the selected function, or [default](https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/default) for `TReturn` when no function is registered and [FunctionInvoker<TReturn>.InvokerNotFoundReaction](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn/) is [FunctionInvoker<TReturn>.InvokerNotFoundReactionType.ReturnDefault](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn.InvokerNotFoundReactionType/). |

### Exceptions

| Type | Description |
| --- | --- |
| `Exception` | Thrown when no function is registered for `transitionName` and [FunctionInvoker<TReturn>.InvokerNotFoundReaction](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn/) is not [FunctionInvoker<TReturn>.InvokerNotFoundReactionType.ReturnDefault](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn.InvokerNotFoundReactionType/). Exceptions raised by a registered function are propagated. |
| `ArgumentNullException` | Thrown when `transitionName` is [null](https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/null). |

### Remarks

If the transition is not registered and [FunctionInvoker<TReturn>.InvokerNotFoundReaction](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn/) is [FunctionInvoker<TReturn>.InvokerNotFoundReactionType.ReturnDefault](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn.InvokerNotFoundReactionType/), [default](https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/default) is returned. Otherwise [Exception](https://learn.microsoft.com/dotnet/api/system.exception) is thrown.

## Nested Types

`protected enum FunctionInvoker<TReturn>.InvokerNotFoundReactionType` 

Defines the behavior when a requested transition function is missing.

[View FunctionInvoker<TReturn>.InvokerNotFoundReactionType](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn.InvokerNotFoundReactionType/)

[Previous ExpressionsUtils](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/ExpressionsUtils/) [Next FunctionInvoker<TReturn>.InvokerNotFoundReactionType](https://api.workflowengine.io/core/OptimaJet.Workflow.Core.CodeActions/FunctionInvoker-TReturn.InvokerNotFoundReactionType/)