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Jeremy.
Nov 09, 2023
Expert Q&A

How to check if a specific function exists within a Move module at a given address?

I'm trying to figure out how to check if a specific function exists within a Move module at a given address in Move smart contract language, and if it does, call that function dynamically. Here's my scenario: I have a vector or array of addresses, and I need to determine whether a particular address has a specific function. If it does, I want to call that function dynamically.

Is there a way to achieve this in Move? I've been struggling to find a solution, and any guidance would be greatly appreciated.

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  • Move Module
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Jackson.
Nov 9 2023, 12:19

Resolving dependencies at runtime, specifically checking for the existence of a function within a module dynamically, is not possible in Move. However, you can determine the existence of a specific resource at a particular address using exists<T>(addr) (more details can be found in the documentation. It's important to note that the resource type T must be known at compile-time. Unfortunately, dynamically calling functions based on their existence within Move module at runtime is not supported in programming language.

If you have any questions, you can ask them here;

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Steven.
Nov 9 2023, 12:27

In Move, there is no built-in mechanism to check if a specific function exists within a Move module at a given address. This is due to the static nature of the language, where all function calls are resolved at compile-time, not at runtime. This means that you need to know at compile-time which functions you're calling and where they are located.

However, you can design your program in such a way that it can handle different types of modules, each of which may or may not implement a specific function. You can achieve this by defining an interface in a Move module that declares the function you're interested in, and then implementing that interface in the modules where the function exists.

Here is an example of how you might structure your code:

address 0x1 {
module Interface {
   public fun specific_function();
}
}

address 0x2 {
module Module1 {
   use 0x1::Interface;

   struct Data has store { }

   public fun call_specific_function() acquires Data {
       specific_function();
   }
}
}

address 0x3 {
module Module2 {
   use 0x1::Interface;

   struct Data has store { }

   public fun specific_function() acquires Data {
       // Implementation of the function
   }
}
}

In this example, Move Module 1 and Module 2 both use the Interface module which declares specific_function. Module2 provides an implementation of specific_function, while Module1 does not. You can then use Module1 and Module2 interchangeably, and call specific_function on them. If specific_function does not exist in the module, the call will fail at runtime.

To handle this, you can use a try-catch block to catch the error and handle it gracefully:

address 0x1 {
module Interface {
   public fun specific_function();
}
}

address 0x2 {
module Module1 {
   use 0x1::Interface;

   struct Data has store { }

   public fun call_specific_function() acquires Data {
       let result = try specific_function();
       // Handle the result
   }
}
}

address 0x3 {
module Module2 {
   use 0x1::Interface;

   struct Data has store { }

   public fun specific_function() acquires Data {
       // Implementation of the function
   }
}
}

In this example, if specific_function does not exist in the module, the try expression will return an error, which you can then handle in the catch block.

Please note that this is a workaround and may not be suitable for all use cases. The Move language is designed to be statically checked, and trying to dynamically check for function existence at runtime can lead to more complex and error-prone code.

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Move is an executable bytecode language used to implement custom transactions and smart contracts.

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