as_variant

A simple Rust macro to convert enums with newtype variants to Options.

Basic example:

```rust use std::ops::Deref;

use asvariant::asvariant;

enum Value { Integer(i64), String(String), Array(Vec), }

impl Value { pub fn asinteger(&self) -> Option { asvariant!(self, Self::Integer).copied() }

pub fn as_str(&self) -> Option<&str> {
    as_variant!(self, Self::String).map(Deref::deref)
}

pub fn as_array(&self) -> Option<&[Value]> {
    as_variant!(self, Self::Array).map(Deref::deref)
}

pub fn into_string(self) -> Option<String> {
    as_variant!(self, Self::String)
}

pub fn into_array(self) -> Option<Vec<Value>> {
    as_variant!(self, Self::Array)
}

} ```