Implementing a Go-Style Select Statement

Go's select statement is a powerful construct for handling multiple channel operations concurrently. It allows a goroutine to wait on multiple communication operations, choosing the first one that is ready. This challenge involves implementing a simplified version of this behavior for learning purposes.

The goal is to create a function that mimics the core functionality of Go's select. This will help you understand how to manage concurrent operations and non-blocking communication patterns.

Problem Description

You need to implement a function, let's call it Select, that takes a variable number of "cases". Each case represents a potential operation on a channel. The Select function should:

1. Wait for any of the provided cases to become ready. A case is ready if its associated channel operation can proceed without blocking.
2. When a case is ready, execute its corresponding action (e.g., receive a value, send a value).
3. Return a value indicating which case was selected and the result of that operation.
4. If multiple cases are ready simultaneously, one should be chosen pseudo-randomly.

For this challenge, we will simplify the types of operations supported:

• Receive cases: These will involve receiving a value from a read-only channel.
• Send cases: These will involve sending a value to a write-only channel.

The Select function should also support a default case, which executes immediately if no other case is ready.

Key Requirements

• The Select function must accept a variable number of Case structs.
• Each Case struct should define the type of operation (send/receive), the channel, the value to send (if applicable), and the action to perform upon successful operation.
• The function should return a boolean indicating if a case was selected (not the default) and the result of the operation (received value or an error if sending failed).
• Implement pseudo-random selection if multiple cases are ready.
• Support a default case.

Expected Behavior

• If a receive case's channel has data, the Select function should receive the data, perform the associated action, and return.
• If a send case's channel is ready to accept data, the Select function should send the data, perform the associated action, and return.
• If no channel operation is ready, and a default case is provided, the default case's action should be performed, and the function should return.
• If no channel operation is ready and no default case is provided, the function should block indefinitely (or until at least one case becomes ready).

Edge Cases

• Empty list of cases.
• Cases involving nil channels.
• Multiple send operations to the same channel.
• Multiple receive operations from the same channel.
• Mixing send and receive operations.

Examples

Example 1: Receiving from a channel

// Assume `ch` is a `chan int` with a value already in it.
// Input:
cases := []Case{
    {
        Operation: Receive,
        Chan:      ch,
        Action: func(v interface{}) {
            fmt.Printf("Received: %v\n", v)
        },
    },
}
// Expected Output:
// Received: <the value from ch>
// The function would return `true, <the received value>, nil`

Example 2: Sending to a channel

// Assume `ch` is a `chan int` that is ready to receive.
// Input:
cases := []Case{
    {
        Operation: Send,
        Chan:      ch,
        Value:     100,
        Action: func(v interface{}) {
            fmt.Printf("Sent: %v\n", v)
        },
    },
}
// Expected Output:
// Sent: 100
// The function would return `true, nil, nil` (or `true, nil, <error if send fails>`)

Example 3: Default case

// Assume `ch1` and `ch2` are empty channels that will not receive data soon.
// Input:
cases := []Case{
    {
        Operation: Receive,
        Chan:      ch1,
        Action: func(v interface{}) {
            fmt.Println("This should not happen")
        },
    },
    {
        Operation: Default,
        Action: func() {
            fmt.Println("Default case executed")
        },
    },
}
// Expected Output:
// Default case executed
// The function would return `false, nil, nil`

Example 4: Multiple ready cases (pseudo-random selection)

// Assume `ch1` has data, and `ch2` is ready for sending.
// Input:
cases := []Case{
    {
        Operation: Receive,
        Chan:      ch1,
        Action: func(v interface{}) {
            fmt.Printf("Received from ch1: %v\n", v)
        },
    },
    {
        Operation: Send,
        Chan:      ch2,
        Value:     "hello",
        Action: func(v interface{}) {
            fmt.Printf("Sent to ch2: %v\n", v)
        },
    },
}
// Expected Output (one of the following, depending on random choice):
// Received from ch1: <value>
// OR
// Sent to ch2: hello
// The function would return `true, <result>, nil`

Constraints

• The number of cases will be between 0 and 50.
• Channels can be of different underlying types, but the Select function will handle interface{} for generic channel operations.
• The Select function should aim for reasonable performance, avoiding unnecessary busy-waiting.
• The Chan field in the Case struct can be nil. Operations on nil channels always block.

Notes

• Consider how you will represent the different operations (send, receive, default). An enum or constants would be suitable.
• You will need to use reflection or type assertions to handle operations on channels of various underlying types.
• For pseudo-random selection, you can use the math/rand package. Remember to seed the random number generator.
• Think about how to signal the completion of a selected operation back to the caller.
• The Action for send cases might receive the value that was sent, and for receive cases, it will receive the value that was received. The Action for the default case will receive no arguments.
• The Select function should return three values: (selected bool, receivedValue interface{}, err error).
  • selected is true if a non-default case was executed, false otherwise.
  • receivedValue is the value received from a channel in a receive operation. It will be nil for send operations and default cases.
  • err will contain any error that occurred during a send operation.