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
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180

//! Deferred value initialization.
//!
//! The [`Fill`] trait is a way to bridge APIs that may not be directly
//! compatible with other constructor methods.
//!
//! The `Fill` trait is automatically implemented for closures, so can usually
//! be used in libraries that can't implement the trait themselves.
//!
//! ```
//! use value_bag::{ValueBag, fill::Slot};
//!
//! let value = ValueBag::from_fill(&|slot: Slot| {
//!     #[derive(Debug)]
//!     struct MyShortLivedValue;
//!
//!     slot.fill_debug(&MyShortLivedValue)
//! });
//!
//! assert_eq!("MyShortLivedValue", format!("{:?}", value));
//! ```
//!
//! The trait can also be implemented manually:
//!
//! ```
//! # use std::fmt::Debug;
//! use value_bag::{ValueBag, Error, fill::{Slot, Fill}};
//!
//! struct FillDebug;
//!
//! impl Fill for FillDebug {
//!     fn fill(&self, slot: Slot) -> Result<(), Error> {
//!         slot.fill_debug(&42i64 as &dyn Debug)
//!     }
//! }
//!
//! let value = ValueBag::from_fill(&FillDebug);
//!
//! assert_eq!(None, value.to_i64());
//! ```

use crate::std::fmt;

use super::internal::{Internal, InternalVisitor};
use super::{Error, ValueBag};

impl<'v> ValueBag<'v> {
    /// Get a value from a fillable slot.
    pub const fn from_fill<T>(value: &'v T) -> Self
    where
        T: Fill,
    {
        ValueBag {
            inner: Internal::Fill(value),
        }
    }
}

/// A type that requires extra work to convert into a [`ValueBag`](../struct.ValueBag.html).
///
/// This trait is an advanced initialization API.
/// It's intended for erased values coming from other logging frameworks that may need
/// to perform extra work to determine the concrete type to use.
pub trait Fill {
    /// Fill a value.
    fn fill(&self, slot: Slot) -> Result<(), Error>;
}

impl<F> Fill for F
where
    F: Fn(Slot) -> Result<(), Error>,
{
    fn fill(&self, slot: Slot) -> Result<(), Error> {
        (self)(slot)
    }
}

/// A value slot to fill using the [`Fill`](trait.Fill.html) trait.
pub struct Slot<'s, 'f> {
    visitor: &'s mut dyn InternalVisitor<'f>,
}

impl<'s, 'f> fmt::Debug for Slot<'s, 'f> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Slot").finish()
    }
}

impl<'s, 'f> Slot<'s, 'f> {
    pub(crate) fn new(visitor: &'s mut dyn InternalVisitor<'f>) -> Self {
        Slot { visitor }
    }

    pub(crate) fn fill<F>(self, f: F) -> Result<(), Error>
    where
        F: FnOnce(&mut dyn InternalVisitor<'f>) -> Result<(), Error>,
    {
        f(self.visitor)
    }

    /// Fill the slot with a value.
    ///
    /// The given value doesn't need to satisfy any particular lifetime constraints.
    pub fn fill_any<T>(self, value: T) -> Result<(), Error>
    where
        T: Into<ValueBag<'f>>,
    {
        self.fill(|visitor| value.into().inner.internal_visit(visitor))
    }
}

#[cfg(test)]
mod tests {
    #[cfg(target_arch = "wasm32")]
    use wasm_bindgen_test::*;

    use super::*;
    use crate::std::string::ToString;

    #[test]
    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
    fn fill_value_borrowed() {
        struct TestFill;

        impl Fill for TestFill {
            fn fill(&self, slot: Slot) -> Result<(), Error> {
                let dbg: &dyn fmt::Debug = &1;

                slot.fill_debug(&dbg)
            }
        }

        assert_eq!("1", ValueBag::from_fill(&TestFill).to_string());
    }

    #[test]
    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
    fn fill_cast() {
        struct TestFill;

        impl Fill for TestFill {
            fn fill(&self, slot: Slot) -> Result<(), Error> {
                slot.fill_any("a string")
            }
        }

        assert_eq!(
            "a string",
            ValueBag::from_fill(&TestFill)
                .to_borrowed_str()
                .expect("invalid value")
        );
    }

    #[test]
    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
    fn fill_fn_cast() {
        assert_eq!(
            42u64,
            ValueBag::from_fill(&|slot: Slot| slot.fill_any(42u64))
                .to_u64()
                .unwrap()
        );
    }

    #[test]
    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
    fn fill_fn_borrowed() {
        #[derive(Debug)]
        struct MyValue;

        let value = MyValue;
        assert_eq!(
            format!("{:?}", value),
            format!(
                "{:?}",
                ValueBag::from_fill(&|slot: Slot| slot.fill_debug(&value))
            )
        );
    }
}