Food spending this month
Requirement
Given a month of ledger transactions — each with a date, category, merchant, and amount — total what was spent in the Food category, and print it as a currency amount. The data is in the code below; both versions must print the line shown under Expected output.
Expected output
Food spending: $84.40
Side by side
Native Dart
FxDart
Why they differ
Native Dart has no "sum of a field" — you either mutate an accumulator in
a for loop or reach for fold with an explicit
seed and combine step. FxDart's sumBy says the intent in one
word, and the filter → sumBy chain reads in the order the
data flows. The gap is small on a two-step task — it widens as steps
are added.
Benchmark
N = 100
Time Tie
Peak memory Tie
N = 10,000
Time Tie
Peak memory FxDart wins
N = 1,000,000
Time FxDart wins
Peak memory FxDart wins
Bars are medians of repeated timed iterations in fresh processes per side (small N is batched for timer resolution). Sides within 5% of each other — or within 0.6 ms, a difference no person can perceive — count as a tie; close relative races are re-measured up to 5 runs. In an app, anything under a few milliseconds is invisible to the user regardless of which bar is shorter. Memory is peak process RSS. The Dart VM and the dataset are identical on both sides, so the difference between the two bars is what the pipeline itself holds onto.