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Turbo Panumarch
Turbo Panumarch

Posted on • Updated on

Solidity: external vs. public & memory vs. calldata vs. storage

It is written in many places how these things are. But what not easy to decide when to use which of them, as it needs a deeper understanding to choose.

So I want to note the quick heuristic methods to choose these.

Public vs. External


So if you know the function you create only allows for external calls, go for external. It provides performance benefits and you will save on gas.

Basically, public means it can be external or internal, the compiler need additional work for the public function. With the external only, it allows arguments to be read directly from calldata, saving the copying step.

Easy read here:

Memory vs. Calldata vs. Storage


  • use calldata when you only need read-only data, avoiding the cost of allocating memory or storage.
  • use memory if you want your argument to be mutable.
  • use storage if your argument will already exist in storage, to prevent copying something into storage over into memory unnecessarily.


To research more

I am still not sure why most of the OpenZeppelin libs choose to use memory over calldata, although they don't mutate them. For example:

Top comments (1)

turboza profile image
Turbo Panumarch

Found this one on why OpenZeppelin team uses memory over calldata.

It seems calldata is limited in functionalities when using with internal function, so they go for memory.