I'm encountering an issue with TypeScript that I'm not sure if it's a bug or an unsupported feature. Here is a Minimal Viable Example (MVE) of the problem:
interface ColumnOptions<R> {
valueFormatter(params: R): string;
valueGetter(params: string): R;
}
const getColumn = function<R>(options: ColumnOptions<R>) {};
getColumn({
valueFormatter: params => 'hello',
valueGetter: params => ({
nr: 1,
str: 'hello',
}),
});
The scenario involves defining an Ag-grid column and aiming to have the parameter of valueFormatter inherit from the return type of valueGetter. In the above case, the parameter type of valueFormatter (R) is automatically inferred as unknown. However, explicitly typing or removing the parameter of
valueGetter</code, like this:</p>
<pre><code>getColumn({
valueFormatter: params => 'hello',
valueGetter: () => ({
nr: 1,
str: 'hello',
}),
});
results in R being inferred correctly. This discrepancy made me consider that there might be a bug in TypeScript, but it could also be an unsupported behavior. I didn't want to raise an issue on GitHub without confirming. The tests were carried out using TS versions 3.8, 3.7, 3.5, and 3.0.