Cheatsheet: let / apply / also / run / with

// |   Function | Receiver | Returns      | Use for                         |
// |-----------|---------|--------------|----------------------------------|
// |   let     |  it     | block result | null-safe scope / transformations |
// |   run     |  this   | block result | compute from `this`               |
// |   apply   |  this   | object       | configure & return same object    |
// |   also    |  it     | object       | side effects (logging, asserts)   |
// |   with    |  this   | block result | non-extension form of run         |

fun main() {
    val s = "  Hello  "

    s.let    { it.trim() }                  // → "Hello"            (transform)
    s.run    { trim() }                     // → "Hello"            (use `this`)
    s.apply  { /* no mutation possible — String is immutable */ }   // → "  Hello  "  (configure & return)
    s.also   { println("about to use $it") }                         // → "  Hello  "  (side effect)
    with(s)  { trim() }                     // → "Hello"            (use as non-extension)
}