The distinctiveness of is, be, has; add

Tripped up today in a discussion of a code change in which I thought an interface implementation was being proposed, where in fact the proposal was to serve up an instance implementing the new interface.

We were discussing an existing class that acted somewhat like a registry, with which the population of instances to be served up was defined at construction time. We needed it to delay resolution of one of the types it was serving up until relatively late – at least, well after construction of the registry.

The phrase that tripped me up was along the lines of: “Add a new interface to the registry, named ISomeFactoryInterface”.

I interpreted this to mean that the registry should implement the factory interface, and had a hard time persuading my counterpart that this was a bad idea.

Of course, it was hard because he was using it to mean has, not is. He thought the registry should be serving up instances of this new interface. That was actually the position I came to too, so in the end we converged anyway.

Interestingly, if he’d used the word has explicitly I might still have misinterpreted to start with. In normal English saying that something “has a certain interface” might imply that it implements that interface.

It reminded me that in the absence of actual code being written down, we have to be really very careful about how we use certain words.