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[hist] Allow TF1 lambdas to receive ndim and npar as arguments - Issue #22071 #22509

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[hist] Allow TF1 lambdas to receive ndim and npar as arguments - Issue #22071 #22509

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fbfce93
[hist] Allow TF1 lambdas to receive ndim and npar as arguments
medeirosdev Jun 7, 2026
5a2d4c0
Update hist/hist/inc/TF1.h
medeirosdev Jun 8, 2026
a74812e
Update hist/hist/inc/TF1.h
medeirosdev Jun 8, 2026
dfda303
[hist] Move fType assignment before if constexpr in TF1Builder
medeirosdev Jun 9, 2026
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21 changes: 18 additions & 3 deletions hist/hist/inc/TF1.h
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Original file line number Diff line number Diff line change
Expand Up @@ -22,8 +22,9 @@
//////////////////////////////////////////////////////////////////////////

#include "RConfigure.h"
#include <functional>
#include <cassert>
#include <cstddef>
#include <functional>
#include <memory>
#include <string>
#include <vector>
Expand Down Expand Up @@ -709,7 +710,14 @@ namespace ROOT {
#endif
{
f->fType = TF1::EFType::kTemplScalar;
f->fFunctor.reset(new TF1::TF1FunctorPointerImpl(ROOT::Math::ParamFunctorTempl<double>(func)));
if constexpr (std::is_invocable_r_v<double, Func, const double *, std::size_t, const double *, std::size_t>) {
auto wrapper = [func, npar = f->fNpar, ndim = f->fNdim](const double *x, const double *p) -> double {
return func(x, static_cast<std::size_t>(ndim), p, static_cast<std::size_t>(npar));
};
f->fFunctor = std::make_unique<TF1::TF1FunctorPointerImpl<double>>(ROOT::Math::ParamFunctorTempl<double>(wrapper));
} else {
f->fFunctor.reset(new TF1::TF1FunctorPointerImpl(ROOT::Math::ParamFunctorTempl<double>(func)));
}
}

f->fParams = std::make_unique<TF1Parameters>(f->fNpar);
Expand All @@ -727,7 +735,14 @@ namespace ROOT {
#endif
{
f->fType = TF1::EFType::kTemplScalar;
f->fFunctor.reset(new TF1::TF1FunctorPointerImpl(ROOT::Math::ParamFunctorTempl<double>(func)));
if constexpr (std::is_invocable_r_v<double, Func, const double *, std::size_t, const double *, std::size_t>) {
auto wrapper = [func, npar = f->fNpar, ndim = f->fNdim](const double *x, const double *p) -> double {
return (*func)(x, static_cast<std::size_t>(ndim), p, static_cast<std::size_t>(npar));
};
f->fFunctor = std::make_unique<TF1::TF1FunctorPointerImpl<double>>(ROOT::Math::ParamFunctorTempl<double>(wrapper));
} else {
f->fFunctor.reset(new TF1::TF1FunctorPointerImpl(ROOT::Math::ParamFunctorTempl<double>(func)));
}
}

f->fParams = std::make_unique<TF1Parameters>(f->fNpar);
Expand Down
24 changes: 24 additions & 0 deletions hist/hist/test/test_tf1.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
#include "ROOT/TestSupport.hxx"

#include <cmath>
#include <cstddef>
#include <iostream>

class MyClass {
Expand Down Expand Up @@ -240,6 +241,29 @@ TEST(TF1, Constructors)
EXPECT_EQ(tf1(&x, &p), 2);
}

TEST(TF1, LambdaWithSizes)
{
// lambda with explicit ndim and npar -- allows safe bound checking inside
auto f4arg = [](const double *x, std::size_t ndim, const double *p, std::size_t npar) -> double {
EXPECT_EQ(ndim, std::size_t{1});
EXPECT_EQ(npar, std::size_t{2});
return p[0] * x[0] + p[1];
};

TF1 f("f4arg", f4arg, 0, 10, 2);
f.SetParameters(3.0, 1.0);

EXPECT_NEAR(f.Eval(2.0), 7.0, 1e-10);
EXPECT_NEAR(f.Eval(5.0), 16.0, 1e-10);

// same but passing via pointer
TF1 fptr("f4arg_ptr", &f4arg, 0, 10, 2);
fptr.SetParameters(3.0, 1.0);

EXPECT_NEAR(fptr.Eval(2.0), 7.0, 1e-10);
EXPECT_NEAR(fptr.Eval(5.0), 16.0, 1e-10);
}

TEST(TF1, Save)
{
TF1 linear("linear", "x", -10., 10.);
Expand Down