Flow error on intersection type when checking child property

Question

Good morning,

today, I had a problem with using a base flow definition and two types that extend the base definition.

There's an array where each element could either match the First or Second type definition. When looping this array, I only want to handle elements matching the First type definition, so I thought it should be done by checking a property that only exists in the definition of First and if this property does not exist, this element should be skipped.

However, I don't get to the point where the check for the property does also tell flow that this property can now be accessed.

I made a small script on flow.org where you can see my problem: https://flow.org/try/#0PTAEAEDMBsHsHcBQAXAngBwKagEIEMBnbAXlAG9FQrQA7PAW0wC5QDkAnASxoHMAaRAF8A3IhQZsAMU7s2oUviKgAZOUrVIMtiwrU9oAG55oAV2asO3fuqqCBIsWiygAypgDGsGgBN5uQtiqutREnj46NvpGpuZsXLwCenZCoohhcpjQmIw0yAQsAILs7HioADzSssigAD6uHl7eAHx+ANqRZLQM5gDkAIw9fKCaVTqGxmYs-T2ggrOJ1J10jFMATIOsDeHk4zFrM3PJALqpmdmYuQQAdJCw7ACieO4AFgAUr2c5yCyVcnVuYW8AEoWAZYJxfMQWsEqCBQL9qhxUExIpxIKBXgBCT4XZA3LTIIE7diYZAmdg0YSzMR6OEAxqgJEovRojGY149EZsGbcUA43JAomdElkilUwQ06hwgAqzxkviZqPRWP5eOehAA8vAaAAFdiwLDsNAcrnIHqC4mk8mU6mRdKwLJXOA8D5ZL74qpA0SCL2IIA

After all, it works when I manually type cast the element to suppress the intersection warning from flow, but in my head, this should not be necessary?

Thanks in advance :)

Answer 1

I now have found a solution and it's actually very simple: Exact object types.

https://flow.org/try/#0PTAEAEDMBsHsHcBQAXAngBwKagEIEMBnbAXlAG8AfRUG0AOzwFtMAuUA5AJwEs6BzADSIKAXwDciFBmwAxbpw6hSlarQB0G-ESG1QkeRzZlVumgDc80AK6t2XXoJOgRQ0RKlZQAZUwBjWHQAJkrkVLoaalqYOrRE-kFGTroW1rYcPPwxNC7C4pLxipjQmMx0yARsAIKcnHioADxyCsigFN5+AYEAfCEA2k5k9Ey2AOQAjCMCegbIRqApNmzjI87OWeRDzEsATJPsHQkbC6O7qzkAuu5FJZhlBGqQsJwAoni+ABYAFJ-XpbOgTUUbR88UCAEo2GZYNxgsQesZdCAATNQFxUCwnNxIKBPgBCX63ZAPGZgjacTDIKycOhiZySRFgEGdVGcdGY7F4z4jfTNFa8UAEspg0mDcmU6m0kT02hIgAq73kwTRGN0WJx+OKfzU70IAHl4HQAAqcWBYThoLk8jgjYVkilUml0pwFWDFNRwPg-TWE4nNMESET+xBAA

What I have found is, that Flow does not exclude type Second from being possible only because there is the property first in it. You need to define the object types to be exact object types in order to check that it can not be Second once there is a first property in it.