Printing for Custom Types
========================
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To use custom types for [`print`] and [`debug`], or convert its value into a [string],
it is necessary that the following functions be registered (assuming the custom type
is `T : Display + Debug`):
| Function | Signature | Typical implementation | Usage |
| ----------- | ------------------------------------------------------------- | ------------------------------------- | --------------------------------------------------------------------------------------- |
| `to_string` | \|s: &mut T\| -> ImmutableString
| `s.to_string().into()` | Converts the custom type into a [string] |
| `print` | \|s: &mut T\| -> ImmutableString
| `s.to_string().into()` | Converts the custom type into a [string] for the [`print`] statement |
| `debug` | \|s: &mut T\| -> ImmutableString
| `format!("{:?}", s).into()` | Converts the custom type into a [string] for the [`debug`] statement |
| `+` | \|s1: ImmutableString, s: T\| -> ImmutableString
| `s1 + s` | Append the custom type to another [string], for `print("Answer: " + type);` usage |
| `+` | \|s: T, s2: ImmutableString\| -> ImmutableString
| `s.to_string().push_str(&s2).into();` | Append another [string] to the custom type, for `print(type + " is the answer");` usage |
| `+=` | \|s1: &mut ImmutableString, s: T\|
| `s1 += s.to_string()` | Append the custom type to an existing [string], for `s += type;` usage |