This translates to:

```ts
declare const userImage: Option;

function getUserImage(): string {
if (userImage._type === "some") {
return userImage.value; // value is accessible here, since _type is 'some'
} else {
return "http://example.com/defaultImage";
}
}
```

## Pattern matching

Pattern matching is a common usecase when dealing with ADTs. You'll often find yourself in a position where you need to default to certain values depending on what the underlying value is. For this reason, we've included a `match` and `matchI` function:

```ts
import { ADT, match, matchI } from "ts-adt";

declare const userImage: Option;

const img = matchI(userImage)({
some: ({ value }) => value,
none: () => "http://example.com/defaultImage",
});

const img = pipe(
userImage,
match({
some: ({ value }) => value,
none: () => "http://example.com/defaultImage",
})
);
```

Both functions work the same way, but their arguments are ordered differently for better inference in different cases.

### Partial Matching

You can also use _partial matching_ if you don't need to match against all possible cases.

Consider if you have an ADT of the shape:

declare const myXor: Xor;
```

You can supply an "otherwise" function which gets invoked if the value doesn't match any of the supplied matchers. The otherwise function will be passed a value whose type is the types which _weren't_ matched.

```ts
declare const myXor: Xor;

matchPI(promise)({ nothing: () => 0 }, (rest) => {
// rest inferred as {_type: 'left', value: number } | {_type: 'right', value: number }
return rest.value;
});
```

## Custom Discriminant field

By default, `ADT` and the `match` functions use the `_type` field as the discriminant. You can build an ADT using a different discriminant field, along with matching `match` functions by using the utilities in `ts-adt/MakeMatch`:

```ts
import { MakeADT, makeMatchers } from "ts-adt/MakeADT";

const [match, matchP, matchI, matchPI] = makeMatchers("typ");
```

You can also use `makeMatchers` to build matchers for ADTs in other libraries:

```ts
import * as O from "fp-ts/Option";

const [match, matchP, matchI, matchPI] = makeMatchers("_tag");