Hardfork version on contracts

[kroggen]

What about letting the smart contracts retrieve which hardfork version the underlying blockchain is running on?

It could be accessed using a function like:

• system.version()

It is useful for contracts to know which functions and modules are available

---

As functions can be added to modules without a hardfork (after V4), the above function can return 2 values:

• hardfork version (major)
• some minor version

  major, minor = system.version()

If the contract is interested only on the first, the it can use just the first value:

  version = system.version()

But this should be possible too:

  if system.version() >= 4 then
    ...
  end

Or return a float in which the integral part is the hardfork version and the decimal part is the minor version, like this: 3.0 4.0 4.1 5.0 ...

[kroggen]

Another option to check if a function is available:

if type(bignum.ispositive) == "function" then
  ...
end

But it only works for functions on existing modules. This will fail if the name_service module is not available:

if type(name_service.resolve) == "function" then
  ...
end

error: attempt to index global 'name_service' (a nil value)

This method checks for the module and for the function:

if name_service ~= nil and type(name_service.resolve) == "function" then
  ...
end

[kroggen]

For implementation, check #270