# Mappings Grammar

### Mappings Grammar

Mapping is a crucial concept for our migrators. It means that from a set of values as input, a function is applied to each value, and generates a set with new values.

It's a powerful tool that allows design mappings by using a syntax quite similar to C#, which is used to transform VB6 code to its equivalent in .NET (C# or VB).

This applies to the following statements:

* Types
* Members (Methods, properties, subroutines, events, among others)

Also, this tool offers the possibility to generate code for statements that are not supported in .NET (for more information, see [Upgrade Stubs](/vbuc/generated-code.md#upgrade-stubs)), reducing the time to carry out the compilation of a migrated project.

In the code below they are some types like `enumAlign` and `ctTips (ctTips1)`, including some members like `Active`, `Tag`, `ToolTipText` and `Alignment`.

**Original VB6 Code source**

```php
Dim enumVal As enumAlign
...
Private Sub setCtTips()
    ctTips1.Active = True
    ctTips1.Tag = "Display component"
    ctTips1.ToolTipText = "CtTips1"
    ctTips1.Alignment = enumVal
End Sub
```

By using Mappings Grammar it is possible to migrate classes and their members to their .NET equivalent.

**Mappings design using Mappings Grammar**

```fsharp
type TipsLib.ctTips => System.Windows.Forms.ToolTip;
type TipsLib.enumAlign => nomap;

member TipsLib.ctTips.Active => Active as boolean;
member TipsLib.ctTips.Container => Container;
member TipsLib.ctTips.Tag => Tag as string;
member TipsLib.ctTips.ToolTipText => ToolTipTitle as string;
member TipsLib.ctTips.Alignment => nomap;
```

**C# Code Generated by VBUC**

```csharp
//UPGRADE_ISSUE: (2068) TipsLib.enumAlign object was not upgraded.
UpgradeStubs.TipsLib_enumAlignEnum enumVal = (UpgradeStubs.TipsLib_enumAlignEnum) 0;
...
private void setCtTips()
{
    ctTips1.Active = true;
    ctTips1.Tag = "Display component";
    ctTips1.ToolTipTitle = "CtTips1";
    //UPGRADE_ISSUE: (2064) TipsLib.ctTips property ctTips1.Alignment was not upgraded.
    ctTips1.setAlignment(enumVal);
}
```

> * *Notes:*
>   * *As shown in the example above, `ctTips` will be upgraded into `System.Windows.Forms.ToolTip`.*
>   * *Some members of `ctTips` class like `Active`, `Container`, `Tag` and `ToolTipText` will be upgrade to its .NET equivalent.*
>   * *There are some classes and members that are not supported in .NET, so it generates stubs; like the class `enumAlign` and the member `Alignment`.*

{% file src="/files/4zeu8h3mhSOpOnuoWPeQ" %}


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