Nested lambda expressions are very slow to compile and generate huge object file by Visual C++
c++, c++11, compiler-bug, lambda, visual-c++
Solution
Not sure how useful such deeply nested lambdas are but for what it is worth as far as I can tell this is a bug, the Visual Studio compiler limits document states (emphasis mine):
The C++ standard recommends limits for various language constructs. The following is a list of constructs where the Visual C++ compiler does not implement the recommended limits. The first number is the recommended limit and the second number is the limit implemented by Visual C++:
and includes the following bullet:
Nesting levels of compound statements, iteration control structures, and selection control structures [256] (256).
If we look at the grammar in the C++ draft standard compound-statement will eventually get back to primary-expression which includes lambda-expression. So Visual Studio should support up to `256` levels of nesting.
You could also see this by looking at the grammar for lambda-expression which is as follows:
lambda-introducer lambda-declaratoropt compound-statement
The draft standard has a set of recommend limits in Annex B but they are only guidelines and do not determine compliance.
Update
The bug report the OP filed was updated recently to indicate this will be fixed in a future release.
Problem
I find that nested lambda expressions are very slow to compile and generate huge .obj files. For example, on my computer, the following code generates a obj file of size 4766 KB: ``` int main() { auto f = [] { auto f = [] { auto f = [] { auto f = [] { auto f = [] { }; }; }; }; }; } ``` And the following code (one more nesting level is added) will cause a C1128 error. ``` int main() { auto f = [] { auto f = [] { auto f = [] { auto f = [] { auto f = [] { auto f = [] { }; }; }; }; }; }; } ``` Also, they are very slow to compile. Is there any explanation for this? I'm using Visual C++ 2013. Update This seems to be a bug in Visual C++, I've reported it to Microsoft: https://connect.microsoft.com/VisualStudio/feedback/details/813755/nested-lambdas-in-visual-c-2013-are-very-slow-to-compile-and-generate-huge-object-file.