src/Schema.php
private function addField(Field $field)
    {
        $fieldName = $field->getName();
        if ($this->hasField($fieldName)) {
            $existingField = $this->getField($fieldName);
            if (!$existingField->isOverridable()) {
                throw new FieldAlreadyDefined($this, $fieldName);
            }

            if (!$existingField->isCompatibleForOverride($field)) {
                throw new FieldOverrideNotCompatible($this, $fieldName, $field);
            }
        }

        $this->fields[$fieldName] = $field;
        if ($field->isRequired()) {
            $this->requiredFields[$fieldName] = $field;
        }
    }
private function addField(Field $field)
    {
        $fieldName = $field->getName();
        if ($this->hasField($fieldName)) {
            $existingField = $this->getField($fieldName);
            if (!$existingField->isOverridable()) {
                throw new FieldAlreadyDefined($this, $fieldName);
            }

            if (!$existingField->isCompatibleForOverride($field)) {
                throw new FieldOverrideNotCompatible($this, $fieldName, $field);
            }
        }

        $this->fields[$fieldName] = $field;
        if ($field->isRequired()) {
            $this->requiredFields[$fieldName] = $field;
        }
    }
@param Field $field

@throws FieldAlreadyDefined
@throws FieldOverrideNotCompatible