Error with trait implementation

gistfile1.txt

error[E0277]: the trait bound `fn(gc::Gc<js::value::ValueData>, gc::Gc<js::value::ValueData>, std::vec::Vec<gc::Gc<js::value::ValueData>>) -> std::result::Result<gc::Gc<js::value::ValueData>, gc::Gc<js::value::ValueData>> {js::string::get_string_length}: js::value::ToValue` is not satisfied
  --> src/lib\js\string.rs:25:14
   |
25 |         get: to_value(get_string_length),
   |              ^^^^^^^^ the trait `js::value::ToValue` is not implemented for `fn(gc::Gc<js::value::ValueData>, gc::Gc<js::value::ValueData>, std::vec::Vec<gc::Gc<js::value::ValueData>>) -> std::result::Result<gc::Gc<js::value::ValueData>, gc::Gc<js::value::ValueData>> {js::string::get_string_length}`
   |
note: required by `js::value::to_value`
  --> src/lib\js\value.rs:632:1
   |
632| pub fn to_value<A: ToValue>(v: A) -> Value {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^