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

use crate::{registry, InputValueResult, InputValueType, Type, Value};
use std::borrow::Cow;

/// Similar to `Option`, but it has three states, `undefined`, `null` and `x`.
///
/// Spec: https://spec.graphql.org/June2018/#sec-Null-Value
#[allow(missing_docs)]
pub enum MaybeUndefined<T> {
    Undefined,
    Null,
    Value(T),
}

impl<T> MaybeUndefined<T> {
    /// Returns true if the MaybeUndefined<T> is undefined.
    #[inline]
    pub fn is_undefined(&self) -> bool {
        if let MaybeUndefined::Undefined = self {
            true
        } else {
            false
        }
    }

    /// Returns true if the MaybeUndefined<T> is null.
    #[inline]
    pub fn is_null(&self) -> bool {
        if let MaybeUndefined::Null = self {
            true
        } else {
            false
        }
    }

    /// Borrow the value, returns `None` if the value is `undefined` or `null`, otherwise returns `Some(T)`.
    #[inline]
    pub fn value(&self) -> Option<&T> {
        match self {
            MaybeUndefined::Value(value) => Some(value),
            _ => None,
        }
    }

    /// Convert MaybeUndefined<T> to Option<T>.
    #[inline]
    pub fn take(self) -> Option<T> {
        match self {
            MaybeUndefined::Value(value) => Some(value),
            _ => None,
        }
    }
}

impl<T: Type> Type for MaybeUndefined<T> {
    fn type_name() -> Cow<'static, str> {
        T::type_name()
    }

    fn qualified_type_name() -> String {
        T::type_name().to_string()
    }

    fn create_type_info(registry: &mut registry::Registry) -> String {
        T::create_type_info(registry);
        T::type_name().to_string()
    }
}

impl<T: InputValueType> InputValueType for MaybeUndefined<T> {
    fn parse(value: Option<Value>) -> InputValueResult<Self> {
        match value {
            None => Ok(MaybeUndefined::Undefined),
            Some(Value::Null) => Ok(MaybeUndefined::Null),
            Some(value) => Ok(MaybeUndefined::Value(T::parse(Some(value))?)),
        }
    }

    fn to_value(&self) -> Value {
        match self {
            MaybeUndefined::Value(value) => value.to_value(),
            _ => Value::Null,
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::*;

    #[test]
    fn test_optional_type() {
        assert_eq!(MaybeUndefined::<i32>::type_name(), "Int");
        assert_eq!(MaybeUndefined::<i32>::qualified_type_name(), "Int");
        assert_eq!(&MaybeUndefined::<i32>::type_name(), "Int");
        assert_eq!(&MaybeUndefined::<i32>::qualified_type_name(), "Int");
    }
}