private DataType getStructFieldType(StructuredDataType structInput) {
        Field field = structInput.getField(structFieldName);
        if (field == null)
            throw new VerificationException(this, "Field '" + structFieldName + "' not found in struct type '" +
                                                  structInput.getName() + "'");
        return field.getDataType();
    }
Returns the value of a struct field.

@author Simon Thoresen Hult
indexinglanguage/src/main/java/com/yahoo/vespa/indexinglanguage/expressions/GetFieldExpression.java