# ref Field

This field serves as reference (alias) to other fields. It can be used to avoid duplication of field definition for multiple messages.

```
<?xml version="1.0" encoding="UTF-8"? version="10">
<schema ...>
    <fields>
        <int name="SomeIntField" type="uint8" defaultValue="Special2">
            <displayName value="Some Int Field" />
            <special name="Special1" val="0" />
            <special name="Special2" val="0xff" />
        </int>
    </fields>

    <message name="Msg1" id="1">
        <ref field="SomeIntField" />
        ...
    </message>

    <message name="Msg2" id="2">
        <ref field="SomeIntField" name="RenamedIntField" />
    </message>
</schema>
```

The **\<ref>** field has all the [common](/commsdsl-specification/fields/common.md) properties. It also copies **name**, **displayName** and **semanticType** [properties](/commsdsl-specification/properties.md) from the referenced field and allows overriding them with new values. Note, that in the example above **\<ref>** field defined as a member of **Msg1** message hasn't provided any **name** value. It is allowed because it has taken a name of the referenced field (*SomeIntField*).

## Referencing the Field

The only extra property the **\<ref>** field has is **field** to specify a [reference](/commsdsl-specification/references.md) to other field.

## Length in Bits

Since **v2** of this specification it is allowed to use **\<ref>** field as member of the [\<bitfield>](/commsdsl-specification/fields/bitfield.md) field while referencing one of the allowed member types. In such case it is required to use **bitLength** property to specify length in bits.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema name="MyProtocol" endian="big">
    <fields>
        <enum name="SomeEnum type="uint8">
            <validValue name="V1" val="0" />
            <validValue name="V2" val="1" />
            <validValue name="V3" val="2" />
        </enum>

        <bitfield name="SomeBitfield">
            <int name="SomeIntMember" type="uint8" bitLength="3" />
            <set name="SomeSetMember" bitLength="3">
                ...
            </set>
            <ref field="SomeEnum" bitLength="2" />
        </bitfield>
    </fields>
</schema>
```

Use [properties table](/commsdsl-specification/appendix/ref.md) for future references.


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