Error Handling

SharpMeter uses a Result<T> discriminated union instead of exceptions for all protocol operations. This makes error paths explicit and composable.

Result<T>

Every async operation returns Result<T>:

var result = await client.ReadTableAsync(1);

if (result.IsSuccess)
{
    var data = result.Value;
    // Use data
}
else
{
    var error = result.Error;
    Console.WriteLine($"[{error.Code}] {error.Message}");
}

Pattern Matching

var output = result.Match(
    onSuccess: data => $"Read {data.Length} bytes",
    onFailure: error => $"Failed: {error.Message}");

Map / Bind

// Transform the success value
var lengthResult = result.Map(data => data.Length);

// Chain operations
var chainResult = result.Bind(data =>
    data.Length > 0
        ? Result<string>.Success("OK")
        : PsemError.Framing("Empty response"));

Error Types

PsemError categorizes errors by source:

Protocol Response Codes

When the meter returns an error, PsemError.ResponseCode contains the L7 code:

if (result.IsFailure && result.Error.ResponseCode.HasValue)
{
    switch (result.Error.ResponseCode.Value)
    {
        case ResponseCode.InsufficientSecurityClearance:
            // Wrong password or access level
            break;
        case ResponseCode.OperationNotPossible:
            // Table doesn't exist
            break;
        case ResponseCode.DeviceBusy:
            // Retry later
            break;
    }
}

Implicit Conversions

Results convert implicitly for cleaner code:

// Success values convert automatically
Result<int> result = 42;

// Errors convert automatically
Result<int> error = PsemError.Timeout("read");