Because instances of Fields can now be meaningfully used by authors after being decoupled from the underlying target. When you call

my_tgt.get(Compatibility)

, you get back an instance of

Compatibility

that no longer knows what the owning target is. That’s intentional - we want Fields to be first class citizens that can be used by multiple distinct target types, eg so that plugin authors can use that same Field without Pants caring that it’s a new target The other key detail is that all field hydration and/or validation is now lazy. We don’t validate

my_tgt.get(Compatibility)

, only

my_tgt.get(Compatibility).value

, where

.value

is a property on the

Field

If our concern was performance, we could stop making

Field

be a frozen dataclass and inject

Address

onto the

Field

only when it was called via

Target.get

. Or, even in

Target.get

, return a new

Field

with the

Address

configured on the frozen

Field

. Both approaches have serious downsides, but avoid storing

Address

on every field used by the Pants run, until we know we actually need those fields