clone method
Implementation
@override
Expression<String> clone(Map<String, ExpressionProviderElement> elementMap) {
return PlusStringExpression(
left.clone(elementMap), right.clone(elementMap));
}
@override
Expression<String> clone(Map<String, ExpressionProviderElement> elementMap) {
return PlusStringExpression(
left.clone(elementMap), right.clone(elementMap));
}