swap in (for someone or something)

1. To act as a substitute for someone or something. After the first quarter, I swapped in for Tom at tight end. Don't believe anyone who tries to convince you that low-fat cooking sprays can swap in for butter or oil without affecting the taste of your food.

2. To use, employ, or instruct someone or something to act as a substitute for someone or something else. In this usage, a noun or pronoun is used between "swap" and "in." With a healthy 30-point lead, the coach swapped the rookie quarterback in to give him some experience on the field. Let's try swapping in a placebo for the active ingredient and see if it changes the outcome.

3. To trade or exchange something for something else. In this usage, a noun or pronoun is used between "swap" and "in." I want to swap a few of my old video games in for the new one that just came out. I always swap in my old phone once the next model becomes available.

4. In computer science, to retrieve a variable in place of some similar or equivalent value. In this usage, a noun or pronoun is used between "swap" and "in." You can use the library function to swap in a single line of code. The host may be swapping in the memory pages of the virtual memory from the swap file.