1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156

//! The `with` macro.
//!
//! This is a macro that takes an object and lets you call methods on that object without naming it.
//! The first argument is an expression that will be assigned to a variable in let binding. To make
//! that binding mutable, prepend `mut` to the expression.
//! Calling a function that starts with a `.` will be converted into a method call using this
//! variable.
//!
//! The supported forms are:
//! - `.method(args..)`
//! - `let pat = .method(args..);`
//! - `var = .method(args..);`
//!
//! Anything else will be evaluated unmodified as an expression.
//!
//! # Example
//! ```
//! use with_macro::with;
//!
//! let vec = with! {
//!     mut Vec::new() =>
//!         .push(1)
//!         .push(42)
//!         .push(-13)
//!         let l = .len();
//!         assert_eq!(l, 3);
//! };
//!
//! assert_eq!(vec, [1, 42, -13]);
//! ```

/// The `with` macro.
///
/// See the module documentation for more details.
#[macro_export]
macro_rules! with {
    // mut expr => ...
    (mut $obj:expr => $($body:tt)*) => ({
        let mut obj = $obj;
        $crate::with!(@parse obj $($body)*);
        obj
    });

    // expr => ...
    ($obj:expr => $($body:tt)*) => ({
        let obj = $obj;
        $crate::with!(@parse obj $($body)*);
        obj
    });

    // termination rule
    (@parse $obj:ident) => ();

    // .method(args..)
    (@parse $obj:ident . $method:ident ( $($args:expr),* ) $($tail:tt)*) => {
        $obj.$method($($args),*);
        $crate::with!(@parse $obj $($tail)*)
    };

    // let pat = .method(args..);
    (@parse $obj:ident let $var:pat = . $method:ident ( $($args:expr),* ) ; $($tail:tt)*) => {
        let $var = $obj.$method($($args),*);
        $crate::with!(@parse $obj $($tail)*)
    };

    // var = .method(args..);
    (@parse $obj:ident $var:ident = . $method:ident ( $($args:expr),* ) ; $($tail:tt)*) => {
        $var = $obj.$method($($args),*);
        $crate::with!(@parse $obj $($tail)*)
    };

    // arbitrary expresion
    (@parse $obj:ident $exp:expr ; $($tail:tt)*) => {
        $exp;
        $crate::with!(@parse $obj $($tail)*)
    }
}

#[cfg(test)]
mod tests {
    use std::cell::Cell;

    #[derive(Debug, PartialEq, Eq)]
    struct Foo(Cell<i32>);

    impl Foo {
        fn new(val: i32) -> Self {
            Foo(Cell::new(val))
        }

        fn get_val(&self) -> i32 {
            self.0.get()
        }

        fn set_val(&self, val: i32) {
            self.0.set(val)
        }

        fn add(&self, n: i32) {
            self.0.set(self.0.get() + n)
        }

        fn mul(&self, n: i32) {
            self.0.set(self.0.get() * n)
        }
    }

    #[test]
    fn basic() {
        let a;
        let foo = with! {
            Foo::new(0) =>
                .set_val(10)
                .mul(2)
                a = .get_val();
                .add(1)
                let n = .get_val();
                assert_eq!(n, 21);
                .mul(2)
        };

        assert_eq!(a, 20);
        assert_eq!(foo.get_val(), 42);
    }

    #[test]
    fn mutable() {
        let vec = with! {
            mut Vec::new() =>
                .push(1)
                .push(42)
                .push(-13)
                let l = .len();
                assert_eq!(l, 3);
        };

        assert_eq!(vec, [1, 42, -13]);
    }

    #[test]
    fn nested() {
        let vec = with! {
            mut Vec::new() =>
                .push(with!{
                    Foo::new(3) =>
                })
                .push(with!{
                    Foo::new(0) =>
                        .set_val(10)
                        .add(3)
                })
        };

        assert_eq!(vec, [Foo::new(3), Foo::new(13)]);
    }
}