expectations

Members

Classes

Unexpected

class Unexpected(T)

An exception that represents an error value.

Functions

expected

Expected!(T, E) expected(T value)

Creates an Expected object from an expected value, with type inference.

missing

Expected!(T, E) missing(E err)

Creates an Expected object from an error value.

Structs

Expected

struct Expected(T, E = Exception)

An Expected!(T, E) contains either an expected value of type T, or an error value of type E explaining why the expected value couldn't be produced.

Templates

flatMap

template flatMap(alias fun)

Forwards the expected value in an Expected object to a function that returns an Expected result.

map

template map(alias fun)

Applies a function to the expected value in an Expected object.

1 import std.exception: assertThrown;
2 
3 Expected!int charToDigit(char c)
4 {
5     int d = c - '0';
6     if (d >= 0 && d < 10) {
7         return expected(d);
8     } else {
9         return missing!int(
10             new Exception(c ~ " is not a valid digit")
11         );
12     }
13 }
14 
15 auto goodResult = charToDigit('7');
16 auto badResult = charToDigit('&');
17 
18 assert(goodResult.hasValue);
19 assert(goodResult.value == 7);
20 
21 assert(!badResult.hasValue);
22 assertThrown(badResult.value);
23 assert(badResult.error.msg == "& is not a valid digit");

• expectations