Ask HN: What is this weird (Flex layout) C++ code?

Obviously, I am way behind in modern C++ syntax past my initial courses. While looking at the WebKit source code in order to understand the flex layout, I see this code: auto performMainAxisLayout = [&] { computeLogicalWidthForFlexItems(flexItems, lineRange, availableLogicalHorizontalSpace, flexRects); distributeMarginAutoInMainAxis(flexItems, lineRange, availableLogicalHorizontalSpace, flexRects); justifyFlexItems(flexItems, lineRange, availableLogicalHorizontalSpace, flexRects); }; performMainAxisLayout(); auto performCrossAxisLayout = [&] { auto availableLogicalVerticalSpace = lineHeightList[index]; computeLogicalHeightForFlexItems(flexItems, lineRange, availableLogicalVerticalSpace, flexRects); distributeMarginAutoInCrossAxis(flexItems, lineRange, availableLogicalVerticalSpace, flexRects); alignFlexItems(flexItems, lineRange, { lineTop, availableLogicalVerticalSpace }, flexRects); lineTop += availableLogicalVerticalSpace; }; performCrossAxisLayout(); This can be seen here[0] for more context. My question is - what is this [&] thing? And I cannot find the method named performMainAxisLayout() or performCrossAxisLayout() defined anywhere in the Layout class either. My assumption was that here, a structure/literal class is being built and the methods are on that class but the Layout class don't have them either. Where can I learn more about this syntax or modern C++ quick overview in general? [0]. https://github.com/WebKit/WebKit/blob/main/Source/WebCore/layout/formattingContexts/flex/FlexLayout.cpp#L506-L536 EDIT: Fixed title typo.