推斷打字稿嵌套泛型類型

Question

我正在嘗試執行以下操作：

function test<
  Feature extends { shape: Geometry; properties: Properties },
  Geometry extends geojson.Geometry,
  Properties extends {}
>() {
  const addFeature = (feature: Feature) => {
    switch (feature.shape.type) {
      case "Point":
        break;
    }
  };

  return {
    addFeature,
  };
}

test<{ shape: GeoJSON.Polygon; properties: {} }, GeoJSON.Polygon, {}>();

有什么辦法不需要傳入第二個泛型和第三個泛型？ 我希望能夠做到這一點：

test<{ shape: GeoJSON.Polygon; properties: {} }>();

並讓打字稿推斷其他兩個泛型

Answer 1

您可以完全省略 Feature defenition，因為它取決於Geometry和Properties

function test<
  Geometry extends GeoJSON.Geometry,
  Properties extends {},
>() {
  const addFeature = (feature: { shape: Geometry; properties: Properties }) => {
    switch (feature.shape.type) {
      case "Point":
        break;
    }
  };

  return {
    addFeature,
  };
}

test<GeoJSON.Polygon, {}>();

或在別處定義

type Feature<G extends GeoJSON.Geometry, P extends {}> = {
  shape: G;
  properties: P;
}

function test<
  Geometry extends GeoJSON.Geometry,
  Properties extends {},
>() {
  const addFeature = (feature: Feature<Geometry, Properties>) => {
    switch (feature.shape.type) {
      case "Point":
        break;
    }
  };

  return {
    addFeature,
  };
}

test<GeoJSON.Polygon, {}>();

但它仍然會有一些問題，如果你有很多 Feature 道具