Async await support in Functions

[aligin]

Hello. I've succesfully integrated DynamicExpresso (.NET Core) in my project, but there is a question with the Functions, that returns Task. Is there support for this kind of Expressions?

Example:

var target = new Interpreter();
Func<int, Task<bool>> func = async (x) => await _someHttpService.Get(x);
target.SetFunction("foo", func);
var parsedExpression = target.Parse("true && foo(1)", parameters));

Currentry I receive Exception

The binary operator AndAlso is not defined for the types 'System.Threading.Tasks.Task`1[System.Boolean]' and 'System.Threading.Tasks.Task`1[System.Boolean]'.

[davideicardi]

Yes, currently this is not supported. Probably this can be written using:

target.Parse("true && await foo(1)", parameters));

Or maybe adding a ParseAsync function ... but unfortunately both methods are currently not supported.

The only solution for now is to rewrite your function with sync methods:

Func<int, bool> func = (x) => _someHttpService.Get(x).Result;

[aligin]

@davideicardi Thanks for the answer. I've already done in sync mode. I realized that the targeted .NET Framework was 4.0. And this version does not contain async await. I think cause of .NET 4.0 suport ParseAsync will be the best choise.

[huangyedie]

Yes, currently this is not supported. Probably this can be written using:

target.Parse("true && await foo(1)", parameters));

Or maybe adding a ParseAsync function ... but unfortunately both methods are currently not supported.

The only solution for now is to rewrite your function with sync methods:

Func<int, bool> func = (x) => _someHttpService.Get(x).Result;

Is it supported now? Async await

[metoule]

No, async / await is not supported, and probably never will be. When you write an async method, the compiler performs a LOT of things (creating a class to hoist captured variables, etc), which can't easily be done.

Under the hood, we're using Linq expression trees, which doesn't provide any method to do that.

You can check this stackoverflow question

[MarcusGoldschmidt]

This is a workaround that worked for me

store the results from the async task before executing the invoke of the Lambda

var interpreter = new Interpreter();

var dictionary = new Dictionary<string, double>();

interpreter.SetFunction("ASYNC_TASK", () => dictionary["ASYNC_TASK"]);

var parsed = interpreter.Parse("ASYNC_TASK() + 1");

// Simulate an async function
dictionary["ASYNC_TASK"] = await Task.FromResult(10);

var result = parsed.Invoke();

Assert.Equal(11.0, result);

Also, you can get the Functions that Lambda contains

List<Identifier> functionsUsedByExpression = parsed
    .Identifiers
    .Where(e => e.GetType().Name == "FunctionIdentifier")
    .ToList();