Bladesinger Extra Attack and Holding Spell

[Gignere]

What are people’s interpretation of how bladesinger’s cast a cantrip with their attack action interact’s holding a spell to cast?

Can you extra attack, cast cantrip, hold it and cast it on a subsequent turn using your reaction?

If this is rules legal this might be a very simple way for BS/Rogue multi’s to get offturn sneak attacks.

[RSP]

What are people’s interpretation of how bladesinger’s cast a cantrip with their attack action interact’s holding a spell to cast?

Can you extra attack, cast cantrip, hold it and cast it on a subsequent turn using your reaction?

If this is rules legal this might be a very simple way for BS/Rogue multi’s to get offturn sneak attacks.

If you’re referring to Ready a Spell, that takes the Ready Action, not the Attack Action, so there’s no interaction between the two.

[Zhorn]

Rsp29a has the right of it, as taking the Ready Action is a whole action in its own right and not part of another.
The particulars of it is you can hold any type of action or movement, so yes you can hold an Attack Action or a Cast a Spell, BUT if they go off on a turn that is not your own then you don't get the benefits that rely on it being your own turn. In the case of the Attack Action that negates Extra Attack, as it is specifying "Starting at 6th* level, you can attack twice, instead of once, whenever you take the Attack action on your turn"
* 5th for most classes, but we're talking Blade Singers so it is 6th for them

So if you want both attacks, or an attack plus a cantrip, it has to be done during your turn, and if during someone else's turn via Ready Action you'll only get one.