Exception handling

Exceptions in Hades

In Hades, everything can be an exception. There is a collection of standard exceptions (in std:exceptions) but nothing prevents you from throwing any object as an exception. This comes in quite handy when you want to handle multiple exceptions with very different error sources.

try-catch-else block

If you want to catch all exceptions, don't specify a type in the catch block.

Example

with client from mssql:client
with server from std:http
with console from std:io
with file from std:io

var connection object = client("Data Source=ServerName;Initial Catalog=DatabaseName;User ID=UserName;Password=Password")
    
try
    connection.open()
    console.out("Connection opened!")
    connection.close()
catch(object::SqlException e) //here, an SqlException is caught
    console.out("SqlException was caught!")
catch(e) //in the case that any other exception was raised, this block is invoked
    console.out("An unknown exception was caught!")
end

try
    file.read("1.txt")
catch(e)
    //ignored
end

try
    var f object::File = file("2.txt")
catch(object::FileNotFoundException e)
    console.out("File {} not found!".format(e.file))
end

let srv = server(port=8080)
srv.get("/:path", {req, res => 
    let path = req.param["path"]
    try
        if (file.exists(path))
            let f = file.open(path)
            res.send(f.read())
        else
            raise 404
        end
    catch(int status)
        res.status(status)
    else
        res.status(200)
    end
})

srv.start()

Code in an else block after a try-catch will be executed if the execution didn't fail.

Example

with console from std:io
var number

try
    number = int(console.in())
catch(e)
    console.out("Could not parse number")
else
    console.out("Number is {}".format(number))
end

raise statement

The raise statement raises an exception.

Example

with exceptions from std:exceptions

func equals(a object, b object)
    if(a == null)
        raise exceptions.ArgumentNullException("{} is null".format(nameof(a)))
    else if(b equals null)
        raise exceptions.ArgumentNullException("{} is null".format(nameof(b))
    end
    
    put a == b
end