Call to constructor of 'TF1' is ambiguous

Newbie
1

Hi,

I got an error while compiling the following code:

#include <Fit/Fitter.h>
#include <TF1.h>
#include <print>

auto main() -> int
{

    auto fitter = ROOT::Fit::Fitter{};

    auto fitted_function = TF1{ "linear",
                                [](const double* variables, const double* parameters) -> double
                                {
                                    auto x_val = variables[0];
                                    return x_val * parameters[0] + parameters[1];
                                },
                                -10,
                                10,
                                3,
                                1 };

    return 0;
}

The error message from clang is:

[3/4] Building CXX object CMakeFiles/main.dir/main.cpp.o
FAILED: CMakeFiles/main.dir/main.cpp.o
/usr/sbin/clang++  -isystem /opt/FairSoft/include/root -std=gnu++23 -MD -MT CMakeFiles/main.dir/main.cpp.o -MF CMakeFiles/main.dir/main.cpp.o.d @CMakeFiles/main.dir/main.cpp.o.modmap -o CMakeFiles/main.dir/main.cpp.o -c /u/yanwang/software/neulandproject/tutorials/root_fitter/main.cpp
/u/yanwang/software/neulandproject/tutorials/root_fitter/main.cpp:10:28: error: call to constructor of 'TF1' is ambiguous
   10 |     auto fitted_function = TF1{ "linear",
      |                            ^  ~~~~~~~~~~~
   11 |                                 [](const double* variables, const double* parameters) -> double
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   12 |                                 {
      |                                 ~
   13 |                                     auto x_val = variables[0];
      |                                     ~~~~~~~~~~~~~~~~~~~~~~~~~~
   14 |                                     return x_val * parameters[0] + parameters[1];
      |                                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   15 |                                 },
      |                                 ~~
   16 |                                 -10,
      |                                 ~~~~
   17 |                                 10,
      |                                 ~~~
   18 |                                 3,
      |                                 ~~
   19 |                                 1 };
      |                                 ~~~
/opt/FairSoft/include/root/TF1.h:425:4: note: candidate constructor [with PtrObj = (lambda at /u/yanwang/software/neulandproject/tutorials/root_fitter/main.cpp:11:33), MemFn = int]
  425 |    TF1(const char *name, const  PtrObj &p, MemFn memFn, Double_t xmin, Double_t xmax, Int_t npar, Int_t ndim = 1, EAddToList addToGlobList = EAddToList::kDefault) :
      |    ^
/opt/FairSoft/include/root/TF1.h:400:4: note: candidate constructor [with Func = (lambda at /u/yanwang/software/neulandproject/tutorials/root_fitter/main.cpp:11:33)]
  400 |    TF1(const char *name, Func f, Double_t xmin, Double_t xmax, Int_t npar, Int_t ndim = 1, EAddToList addToGlobList = EAddToList::kDefault) :
      |    ^
/opt/FairSoft/include/root/TF1.h:357:4: note: candidate constructor
  357 |    TF1(const char *name, Double_t (*fcn)(const Double_t *, const Double_t *), Double_t xmin = 0, Double_t xmax = 1, Int_t npar = 0, Int_t ndim = 1, EAddToList addToGlobList = EAddToList::kDefault);
      |    ^
1 error generated.
ninja: build stopped: subcommand failed.

Thanks for your attention

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ROOT Version: 6.36.04
Platform: fedora 42
Compiler: clang 20.1.8

2

The xmin and xmax above are taken as integer, which confuses the constructors with lambda. Try defining them as double or Double_t variables and use the variables in TF1 instead of numbers, or maybe do:

...
                                -10.,
                                10.,
                                3,
                                1 };