使用不可构造类型的 TypeScript 中的丰富编译时异常

// create a unique symbol for our type exception
declare const typeexception: unique symbol;

// basic type definitions
type struct = record<string, any>;
type funct<t, r> = (arg: t) => r;
type types<t> = keyof t & string;
type sanitize<t> = t extends string ? t : never;

// the core pattern for type-level exceptions
export type unbox<t extends struct> = {
    [type in types<t>]: t[type] extends funct<any, infer ret>
        ? (arg: ret) => any
        : t[type] extends struct
        ? {
              [typeexception]: `variant <${sanitize<type>}> is of type <union>. migrate logic to <none> variant to capture <${sanitize<type>}> types.`;
          }
        : (value: t[type]) => any;
};

type datavariant = 
    | { type: 'text'; content: string }
    | { type: 'number'; value: number }
    | { type: 'complex'; nested: { data: string } };

type varianthandler = unbox<{
    text: (content: string) => void;
    number: (value: number) => void;
    complex: { // this will trigger our custom error
        [typeexception]: `variant <complex> is of type <union>. migrate logic to <none> variant to capture <complex> types.`
    };
}>;

// this will show our custom error at compile time
const invalidhandler: varianthandler = {
    text: (content) => console.log(content),
    number: (value) => console.log(value),
    complex: (nested) => console.log(nested) // error: type has unconstructable signature
};

type treenode<t> = {
    value: t;
    children?: treenode<t>[];
};

type treehandler<t> = unbox<{
    leaf: (value: t) => void;
    node: treenode<t> extends struct
        ? {
              [typeexception]: `cannot directly handle node type. use leaf handler for individual values.`;
          }
        : never;
}>;

// usage example - will show custom error
const invalidtreehandler: treehandler<string> = {
    leaf: (value) => console.log(value),
    node: (node) => console.log(node) // error: cannot directly handle node type
};

type loadingstate<t> = {
    idle: null;
    loading: null;
    error: error;
    success: t;
};

type statehandler<t> = unbox<{
    idle: () => void;
    loading: () => void;
    error: (error: error) => void;
    success: (data: t) => void;
    // prevent direct access to state object
    state: loadingstate<t> extends struct
        ? {
              [typeexception]: `cannot access state directly. use individual handlers for each state.`;
          }
        : never;
}>;

// this will trigger our custom error
const invalidstatehandler: statehandler<string> = {
    idle: () => {},
    loading: () => {},
    error: (e) => console.error(e),
    success: (data) => console.log(data),
    state: (state) => {} // error: cannot access state directly
};

// The [TypeException] property creates an unconstructable type because:
// 1. The symbol cannot be constructed at runtime
// 2. The property is a template literal type containing useful information
// 3. TypeScript will try to unify this type with any attempted implementation

// When you try to implement a type with TypeException:
type Invalid = {
    [TypeException]: string;
};

// TypeScript cannot create a value matching this type because:
// - The TypeException symbol is not constructable
// - The property type is a literal template that cannot be satisfied
const invalid: Invalid = {
    // No possible implementation can satisfy this type
};