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// In TypeScript, we'd use the infer keyword:
// type ReturnType<T> = T extends (...args: any[]) => infer R ? R : never;
// type ElementType<T> = T extends (infer U)[] ? U : never;

// Example functions with different return types
function greet() { 
  return "Hello, world!"; 
}

function getNumber() { 
  return 42; 
}

// Simulating ReturnType
function getReturnType(fn) {
  const result = fn();
  return typeof result;
}

console.log("Return type of greet:", getReturnType(greet)); // string
console.log("Return type of getNumber:", getReturnType(getNumber)); // number

// Simulating ElementType inference
function getElementType(arr) {
  if (arr.length === 0) return "unknown";
  return typeof arr[0];
}

console.log("Element type of number array:", getElementType([1, 2, 3])); // number
console.log("Element type of string array:", getElementType(["a", "b", "c"])); // string

// In TypeScript, this would be handled at compile time
console.log("In TypeScript, the type 'ReturnType<typeof greet>' would be: string");
console.log("In TypeScript, the type 'ElementType<number[]>' would be: number");

Return type of greet: string
Return type of getNumber: number
Element type of number array: number
Element type of string array: string
In TypeScript, the type 'ReturnType' would be: string
In TypeScript, the type 'ElementType' would be: number